I really don't understand how people say that "youtube is collapsing gahh run blah blah". Now don't get me wrong, regardless of me not caring about the comments and as of yet I am completely unaffected by the content ID changes, it's a pretty proposterous accusation. Gamers do currently make up a good proportion of the top and rising channels, but I can assure you from the 5 or so years of spending many a weekend on youtube, there are so many other popular channels outside this category.
All things considered this a massive site and yes this was true of myspace, but I kind of feel that the community and such is too strong, and too tied to mainstream media to just dissipate.
If I was to hazard a guess as to how it may die my theory is as such:
Many youtubers are transitioning to subbable, a similar site allowing for crowdfunding type revenue, rather than ad based. If enough youtubers transfer and make profit there will be less youtube traffic. In my eyes, one of the main draws of youtube is the low entry level allowing for anyone to start. With decreasing traffic and decreasing views low end e.g. <100 subbed channels stop posting and may also stop viewing. This means the middle band channels (say 1,000-50,000 subs) stay on, but may transition to subbable if they feel that they can do better. Ultimately the platform may not die out, but most of creators will and while it won't kill the platform it would be maimed to say the least.