Vedui your attack fails to damage the rat swarm, but you manage to retreat just in front of the swarm without being overwhelmed.

Jormund, by helping Firth, you and him are both able to dash, and you succeed in moving another 30ft toward the exit as you bodily haul Firth down the tunnel as fast as he can go.  You are now 75 ft from the tunnel exit. 

Ann, do you take any action? You see Jormund rush by you with a man in guard's armor leaning heavily on him, while Vedui attempts to stave off the oncoming hoard of rats, and Bryn appears to be searching the tunnel for anything he can use to aid your situation. You also hear incantations from the far end of the tunnel, but without darkvision, you cannot see their source. 

Jormund calls back to Ann, "Coming?! Follow me..." He then proceeds to rush Firth to the exit.

CON check 7

In the sight of what, or in this case, who's coming her way, Ann is ready to hold her ground so as to give others time to escape, and the look on her face makes that obvious. However, hearing Jormund's voice, she wastes barely a second keeping to that idea, as she turns around and follows, hoping to also get a hold and help carry Firth out.

Bryn pulls on the root with all his weight once Vedui is safely passed him.

Bryn, give me a strength check please.

STR: 10

PC2 Round 2

Bryn, you furiously tug on the root, trying to dislodge it, and eventually work it somewhat loose, and a shower of dirt falls around you. Since you didn't completely rip out the root, the tunnel remains passible, but that 5ft portion becomes difficult terrain. You think you could block it fully if you were able to pull the root out completely, but can you do it before the rats get to you?

Vedui, you take a defensive stance and make a fighting retreat at the very edge of the oncoming swarm.  Your blows fail to take purchase on the rats, but you remember your previous rat encounters, and take a defensive stance, crouching low and sweeping your spear like a scythe in front of you, warding yourself from attack. As you retreat, you bump into Bryn who has been desperately pulling on a loose root in the ceiling, and you carefully back over the debris accumulating on the floor.

The rat swarm is now immediately behind Bryn and Vedui, and Ann, Jormund, and Firth are 60ft up the tunnel. 

Jormund and Ann, together you assist Firth towards the exit of the shaft, and although you are winded from the exertion Jormund, with Ann's help you are able to move 30ft closer to the exit, which is now only 45ft away. 

Complication:

12 No complications occur this round.

End PC Round 2

Begin NPC Round 2:

Rats continue to dash at you, 10 succeed their Con check, and reach the square directly beside Vedui. They gnash their teeth warily at your sweeping spear, but cannot reach you this round. 

The Cloaked figure will move forward behind the swarm of rats, and suddenly a flash of flame will appear in his hand, and he will toss a streak of flame toward Vedui.  Attack: 10 Damage: 3, but you deftly duck out of the way without trouble. 

End NPC Round 2

It is now the PC's turn again!  What do you do, with the rats pressing close to on the elven duo, while the rest of the team attempts to rush Firth out of the tunnel?

Begin PC Round 3.

Edit: Bryn and Vedui, can you give me a perception check, as you briefly see the cloaked figure illuminated by his own flame. 

perception  12

Vedui is going to do a stomp dance on the rats nearest him now, kicking as they get close  "Bryn, did you happen to bring any lantern oil?  Some fire would be nice now"

Attack: 25 Damage: 9

bonus action attack Attack: 18 Damage: 7

"Nope, never needed it. Mind giving me a hand with the root?"

Bryn continues to tug at the root. STR: 2

Perception: 20

(Well at least I got one good roll.....)

(OOC - heading out for a 3 day camping trip on Friday will be back Sunday afternoon CST. Bryn’s goal is to get everyone out of the sewer safely if he needs to be bot’s)

Ann has a different plan, looking at the situation. "I can get him there really quickly. You can keep following us or stay behind to help the other two." She takes the responsibility to carry Firth all by herself, and will, if needed, even use an Action Surge to get there that much faster.

(So, basically, taking 2 dashes while at base 40 ft. speed. Again, only using Action Surge if it's necessary to get there this turn.)

Bryn and Vedui, as the flash illuminates your vision, your see the face of the red cloaked figure illuminated in a flash of fiery light.  You see a thin, elvish face, but covered by tattoo's of swirling patterns and arcane sigils, and a distinctive white curl of hair flowing in front of his face. You could now easily pick this person out from a crowd.

Vedui, your vicious a flurry of kicks and pounding causes the rats to temporarily recoil in alarm, and form a hissing, roiling mass that appears to be working up the courage to attack again. With your nat20, You've given them disadvantage on their next attack vs you and Bryn, and temporarily stopped their advance.

Bryn, that stubborn root refuses to budge, despite your best efforts. 

Jormund, is there anything you'd like to do besides dash to the exit?  If you choose to dash, please give me a con check to continue dashing, otherwise, tell me how you help the party in this chase.

Ann, Currently Firth's movement speed is 15ft per round. If you assist him, he can dash 30ft.  If you'd like to carry him bodily, you will be encumbered by his weight and have difficulty moving, so I'd say that your speed will be reduced by half unless you succeed on a DC 15 Strength check. 

So give me a con save to be able to Dash, DC 11, and a strength check DC 15 to see if you can use your full movement speed while dashing. If either fails, you can use your action surge to attempt to dash again. 

Vedui, seeing what Brynn is trying will give aid to his action to remove the root.

Constitution save: 14

Strength Check: 4

EDIT:

Ann has the energy to keep going despite the weight, but she's not exactly strong, always priding herself on her speed more. Still, her plan did involve pulling on the extra energy only she had. (Using Action Surge)

Constitution Save: 24

Jormund sees that Ann has taken Firth. He pivots and moves towards the rats and the caster at normal speed. He then fires a guiding bolt at the caster (ooc assuming I can still see him and he’s within 120ft).

Action: guiding bolt 13

Jormund that hits, roll damage.

"Thank the Maker." The guiding bolt does 14 damage.

Hey guys, sorry for the delay in response, work is taking me into the office more often. 

PC Round 3:

Jormund, tired of running from his shadowy pursuer, channels the light of the forge into a bright streak of flame and light, which clings to the red-cloaked figure, seeming to illuminate and predict his movements.  The next attack against him will have advantage, and he has received a total of 28 damage. 

Bryn, continues to strive mightily with the root protruding from the bottom of the tunnel, but still receives nothing but a light shower of dirt for his troubles. 

Vedui is staving off the rat swarm from Bryn with a flurry of kicks, succeeding in buying him a few precious seconds through his furious dance of death. 

Ann, digging deep into her inner reserve of strength, transports Firth to the base of the ladder to climb out of the sewer with great haste.  They now face a 30ft climb using the rotted ladder and the rope you descended on. 

NPC Round 3:

Hissing in pain and frustration, the red-cloaked man with arcane sigils now illuminated by the tempering fire of the forge, will retreat down the hall away from you and disappear around the corner. He has received a total of 28 damage. 

The rat swarm is now upon you Bryn and Vedui. They roil over your bodies and inside your clothes, and you begin to be assailed by a thousand tiny bites and scratches, amidst a chorus of mad chittering screeches. 

Each round you are in the swam, which is mechanically equivalent to 8 rat swarms, only a portion of the swarm can attack you at any time, so I will roll an attack roll against each of you. 

Against Vedui: Attack: 3 Damage: 5

Against Bryn : Attack: 12 Damage: 4

Chase Event 5

Your comrades on the surface have been busy. Ann, when you reach the manhole, you discover that while your team was exploring, the guards watching the tunnel entrance had run to a nearby 2 story building and grabbed the ladder used for roof access, and are placing it in the hole.  The DC for climbing out is reduced.

End NPC Round 3:

Begin PC Round 4:

What do you guys do next? Bryn, you can still attempt the strength check if you wish, there is no failure threshold.

Vedui is going to aid Bryn, giving him advantage....