It's FUD only if you deny the risk of Microsoft behaving badly. It's entirely possible Microsoft's legal staff is larger than the whole Mono developer base. Whether Microsoft crushes Mono is irrelevant to me - I have long migrated away from Windows and, while Gnome seems to use Mono a lot, I can also migrate away from that. It's my advice, however, to never, ever, under no circumstances, trust Microsoft to do the good thing. It's behaviour is highly predictable and I am yet to see a single sign it even can act like a good corporate citizen.
"The .NET compilers costs absolutely nothing and are part of the free (as in beer) .NET SDKs"
True. You can develop for Windows with .NET without Visual Studio.
"Even if Microsoft wanted to bail out at this point, it would be too late."
Microsoft can bail out any time it wants. All they need is to come out with a "new and improved" API and a "new and improved" Visual Studio that are both slightly forward-incompatible with what Mono needs. Windows developers will flock to the new platform while Mono developers will struggle to make Mono compatible again. And do so every time Microsoft wants to. Mono developers really work for Microsoft.
The scenario where Mono declares independent and follows a distinct path is as reasonable as expecting Mac developers to develop against GNUStep (which is really fine) instead of using Xcode. It won't happen and it won't be able to steer the reference for compatibility a bit. As ECMA-sanctioned (which is sort of meaningless) as they are, the real standard, the one the market follows, is the one dictated by Redmond.