Part of me is tempted to VTC as too broad, but I'll bite.
Netscape didn't really die (Modern day firefox is a literal descendant of it). It didn't innovate, and a competitor with deep pockets, a willingness to innovate (and yes, there was a period where IE was actually innovative) and the ability to get market penetration quickly through many means took it on.
In a sense, outside being the victor (and if you think about it, SE had a free, arguably superior product - which is what won MS the first browser war, there were few parallels.
Kazzaa and napster were basically killed off by media companies and laws. They did not die solely due to being an inferior product.
The chat systems mentioned had similar reasons for dying . ICQ got killed off cause AOL bought it. MSN messenger got killed off cause MSN bought skype. So, as long as SE dosen't get bought over by a bigger company with a similar product with better product recognition, we should be safe
MSN's internet gaming... what? Let me look that up. Wikipedia says it is still around
And well, most of these is relatively irrelevant. SE really only needs two things to survive.
I'd note, most of this is speculative. I'm not an SE Employee at the point of writing, and none of this information is in any way, stuff I picked up as a mod.
Firstly, It needs a steady revenue source - Stuff like SO Enterprise and SO Jobs are aimed at creating that. Least from the job postings (Which I admit to looking at regularly!), there's pretty heavy investment in people to do marketing and engage possible customers on those fronts. In a sense, SE cannot keep the lights on without paying the lighting bills. This kills off many companies, but hopefully SE can avoid this
Secondly, it needs to keep users engaged - this is tricky. Folks on the internet are a prickly bunch. Too much change and they get annoyed. Things being too much the same means people get bored and drifting off. There's also the occasional mass exodus of users (which happens some times). Some sites also end up getting users chased off by folks who want to troll or are a bit too grumpy. A massive part of keeping a service like this up is about soft skills, and finding the right folk to help run the various sites, and keeping a core of users who can both provide good content, and help with meta moderation. This is closer to the problems of keeping a forum or message board running than say a chat or any of the examples you gave.
SE does have a few flaws. At the moment, I feel the strategy for finding the 'next big product' feels scattered, and that SO is not the best place for it, even if SE's been billing itself as a little more developer centric than it felt like when I was new. I admit - going beyond QA is important, just that for the rest of SE, we don't know where things are going sometimes. We haven't quite hit DICE era slashdot unhappiness, but I think I've complained somewhat loudly about things before. I personally don't like the SO pivot (as someone who's spent more time on the rest of the trilogy) - but I get the goals here in terms of branding, and its a semi trivial thing to change back, if the SE brand proved better.
To sum up - stagnation - the inability to grow, both in terms of revenue, and users or getting acquired by a larger company (or even an internal pivot) that doesn't see the value in QA could kill off SE.