RAW Question: if you become unconscious while wearing these, do you:

• fall and hit the ground taking damage (or death saving throw),
• hover (0 speed) or
• fall at 30 ft/sec,

These are cool in every way.

30 feet per round.. you fall and take damage

ur fine, it is not a conditional effect

30 feet per round.. you fall and take damage

Assuming that the boots continue to function after the wearer is incapacitated, and going by the principle that a round is equivalent to 6 seconds, so you'd fall at 5 feet per second, (30 divided by 6).

Assuming gravity in the world of DnD is similar to that of here on Earth, falling accelerates at approximately 32 feet per second squared. Hitting the ground at 5 feet per second is mathematically equivalent to hitting the ground after falling from a height of 4.7 inches.

I'd say that means you wouldn't take any fall damage under normal circumstances.

Falling

A fall from a great height is one of the most common hazards facing an adventurer. At the end of a fall, a creature takes 1d6 bludgeoning damage for every 10 feet it fell, to a maximum of 20d6. The creature lands prone, unless it avoids taking damage from the fall.

You fell 30 feet in a single round.  You would take 3d6 fall damage.  Thems the rules as laid out by the DMG

The item description is "If you are flying when the duration expires, you descend at a rate of 30 feet per round until you land", not "you fall at a rate of 30 feet per round and take damage".

I was simply doing the math for fun as to how hard hitting the ground at 30 feet per 6 seconds would be, and in the answer is that in the real world, it would not be enough to be hurt.

The item's description clearly indicates that the character descends and lands when the effect expires, and it doesn't stipulate any different behavior if a player is incapacitated. If the boots were destroyed it might be another matter, and I'm sure a DM can apply their own discretion.

So what your saying is to ignore the rules of the game as laid out by the Dungeon Master's Guide?

I'm not debating how fall damage works, I'm pointing out that the item description explicitly notes that when the duration of the effect expires, the character wearing them descends and lands (safely), without falling. Since it does not make any exception for the state of the character, it can be expected that this is how the item works any time its magical effect ceases to function.

This is direct contrast to, for example, the Fly spell, which explicitly states "when the spell ends, the target falls if it is still aloft, unless it can stop the fall". Conversely, these boots do not require casting or concentration like the Fly spell, and they are explicitly described to descend and land when the magic wears off, so I'm not sure why anyone would assume that the wearer becoming incapacitated while wearing them would cause them to fall and take damage as if they were using the Fly spell under the same circumstances. These are magically enchanted Winged Boots, not Boots of Cast Fly.

That was fantastic!

Most relevant rule section is PHB Ch 9, "Flying Movement".

...If a flying creature is knocked prone, has its speed reduced to 0, or is otherwise deprived of the ability to move, the creature falls, unless it has the ability to hover or it is being held aloft by magic, such as by the fly spell.

DM discretion, obviously.  But I've ruled:  Mechanically they give you an innate fly speed (see the item "notes" section).  They aren't magically holding you aloft themselves, they aren't sentient.  You need no action, but do need to be conscious to command them.  You getting knocked out, restrained, paralyzed, etc is NOT equivalent to "duration expired."  That is only for the 4 hour duration being hit.

Ergo: You can fall when wearing these boots, like any other creature with innate fly speed. 

Game balance point: it is only an uncommon magic item.  Compare to other such items, this is a fair adjudication of its power.

That is the 'escape velocity', the initial speed an object needs given no other propulsion to escape a bodies gravitation influence.  This is the speed you need if, say, you are fired out of a cannon.  If a creature has a fly speed they can continue to propel themselves.  Now winged boots might require atmospheric pressure to use that fly speed, but if the fly speed is magically imparted then you cold just very slowly make your way into space.

Honestly, if you dont use them to just fly around with no purpose, the 4 hour limitation is almost neglectable. 

if we just assume Battles, which will mostly take only 1-2 minutes, we are talking about 120 Battles until the Boots run out of juice, and other Situations that requier flying should also be able to be solved in 1 or 2 minutes. 

Which means, you will almost certainly reach a save destination to have 1 day of downtime, which will recharge the boots to full. 

So yeah, just dont fly around just for the fun of it and you basically just have a flying speed whenever you need it.

Not if you're an Air Genasi Monk, you can rest the boots with the levitate cantrip and move up further that way. And if you fall you have slow fall and monk ability to reduce fall damage.

Could you theoretically carry someone else while flying? there's not a weight limit listed so I started scheming immedietly

I think that the debate I need here for an answer is this just part of your movement you have or is it extra gained movement?

These will be really good for my wood elf monk :)

How are these not a legendary item?

I was gifted these in a campaign by another PC. My PC tried them on, failed the con save for trying them out and started flying themselves into walls! Another PC removed one of the boots, and my PC started spinning in the air! It was a wonderfully funny session! 

There is no such Con save...