I'm sure this is already pointed out in the thread: but Bitcoin is more than the code that runs it. Bitcoin is an idea with a set of universally accepted properties: 21 million units of currency, decentralized, bla bla bla.

If this dooms day scenario of yours were to be played out then the resulting work wouldn't be Bitcoin and everyone would switch to a version of the code that was. That is the advantage of open source: we all have access to the internals of Bitcoin and version control tracks all changes. We're not using the Bitcoin code because we -have- to -- we're using it because we want to, and what you suggested is something no one would want. So in essence, the perceived "control" that the core developers have over Bitcoin is based on being able to do what the majority of people consistently want. Thus, there isn't a way to control Bitcoin without also controlling the majority of its participants. Satoshi thought of that too.

In conclusion, so long as people think Bitcoin should be like... well Bitcoin - then it shall be. (The idea itself is decentralized )