I think you're right: Too often, people underestimate the power of creditors in industry. If there's
any potentially valuable IP, no matter how outdated, it becomes increasingly unlikely older releases will be supported or patched. I suspect you're also correct regarding the legal issues: In many cases, licensing agreements were made between the
now defunct company, and others, which may or may not carry over. Often, even the licensors themselves may have been acquired, and discovering who actually
owns what becomes expensive or prohibitive. Worse, on rare occasion, the parties involved are dead.
Nevertheless, there are sometimes happy endings, and I'm reminded of this comment [1] by Don Hopkins just over a week ago highlighting the importance of equal parts archivists' duties, detective work, and persistence (very much worth reading) with a healthy dose of luck. Unfortunately, this is probably more an exception than the rule, though older/niche games are perhaps more likely to survive through such efforts than popular ones (Carmageddon's resurrection with the new Stainless comes to mind) given that there's less at stake.
If a much more popular franchise goes belly-up, I would be exceedingly surprised if independently playable versions were ever released. More likely, you'll see new installments based on the same IP with the same shortcomings, thus repeating the cycle. Tribes is a curious, if complicated example (failure, resurrection, failure, resurrection), but it's also a case where an interested third party was able to circumvent the authentication server code (Tribes 2 via TribesNext).
[1] https://news.ycombinator.com/item?id=13693675