We all love talking about how much we want, say, E.A to disintegrate, but why not go the other way for a bit. 

Imagine that tomorrow, a major third party developer suddenly vanished. No more games, no more projects, nothing. 

Which one would have the worst affect on the industry as a whole. 

(Note when I say this, I do mean developers who release a fair few games a year. So something like Project Redd or Rockstar aren't really applicable here.

I can't think of any single developer off of the top of my head, but publisher, probably Take-Two interactive.

Can't think of anyone as far as developers specifically go, but as a publisher, probably Bethesda as without them the Switch wouldn't have Doom, Wolfenstein II, or Skyrim.

No one really, every single publisher/developer (and that includes Sony, Nintendo and MS) is replaceable .

Ubisoft? 

Capcom!

Capcom.

Replaced by what? When Resident Evil is gone a third class eastern european dev can simply fill the void with their cheap RE knock off?

Can you imagine the sudden chaos in the gaming world if GTAs would suddenly stop being made?

I'd only weep for studios that bring something unique and cannot be replaced easily. The only studio that comes to mind is Square Enix, because they're the only ones willing to create AAA JRPGs on a regular basis. Wouldn't weep a tear for anyone else. (well, maybe Psyonix)

Losing Square Enix would suck the most.