So in a session that i have on hold until next session.... I have one player that is on the back of a wyvren already 190 feet up in the air. The only one in the party that possibly can fly is the Druid who is currently at 1hp. how and what could be a possible attempt to catch him if he falls off this thing?

If the Druid still has at least one use of Wild Shape or Polymorph, he/she could transform in a big enough flying creature (Giant Eagle comes to mind) and catch the falling comrade, as being at 1hp would count little considering the buffer hp gained from either option.

If those options are a no go due to level or other circumstances... I hope there's at least a body of water at the end of those 190 feet, otherwise the falling hero is in for quite a hurt.

We had a warlock with the same problem. Falling down from a wyvern at a high place.

He used Misty Step to teleport 30" up when he almost hit the ground.

Then he just got falling damage for the 30" instead of 200"

awesome thank you guys you are both terrific! 

I note he hasn't actually fallen off yet......perhaps he should prioritise better?

Otherwise, turning up for the session with a freshly cooked pizza and a twelve pack would be my fallback plan....

Alternatively:

This method is a bit game-y, and not something I usually like to do, but...  As per Xanathar's Guide, falling is 1d6 per 10 feet.  So, jumping from this height would be 19d6 damage, or about 70 damage.  For instant death to apply, you need to not only reduce the PC to 0 hp, but deal an additional amount of damage equal to total HP again.  So, someone with 35 hp would just survive if they took 69 points of damage.  Someone with 45 hp would need 90 damage, etc.  So, in this scenario, if the PC has more than 35 HP, this would likely not outright kill her or him, and give a healer time to cast something to stabilize the character.  Spare the Dying, Healing Word, etc.

Quote from Mephista>>

Alternatively:

This method is a bit game-y, and not something I usually like to do, but...  As per Xanathar's Guide, falling is 1d6 per 10 feet. 

So, jumping from this height would be 19d6 damage, or about 70 damage. 

For instant death to apply, you need to not only reduce the PC to 0 hp, but deal an additional amount of damage equal to total HP again.  So, someone with 35 hp would just survive if they took 69 points of damage.  Someone with 45 hp would need 90 damage, etc.  So, in this scenario, if the PC has more than 35 HP, this would likely not outright kill her or him, and give a healer time to cast something to stabilize the character.  Spare the Dying, Healing Word, etc.

The Xanathar's guide rule just clarifies how long such a fall takes. Anything under 500 feet will occur in one round.