I think the best thing to hope is that the Volition team would be heavily involved if FS3 was made by other developers. Heck, maybe the team could do what the people behind the new Sam & Max games did- they left and made their own company. If not, the next best thing is if the new developers decided to make a prequel, so then they wouldn't be trying to answer the questions from the end of FS2 themselves, and thus wouldn't be accused of raping the IP by a bunch of FS zealots.
Another hope is that some of the original Volition people go off and make a "spiritual successor" to FS, not to mention revive the genre. I've noticed that sort of thing happening a lot lately. Witness, say, Supreme Commander.
I guess the thing about Fallout and Freespace is that the sequels were bigger and better than the original. Other franchises don't always have that luxury. A lot of people were angered by the dummying-down of Deus Ex: Invisible War, so even of DX3 turns out to be different from that, it's not as if they can say that it was the fault of a lack of Warren Spector.
The people who accuse Bethesda of ruining the Fallout series- well, I can see the point, but if they make a quality game, at least the series gets new fans, doesn't it? The NMA zealots, people who call the new (and excellent) Battlestar Galactica series "Galactica in Name Only", and so on- I understand their anger, but c'mon. If it's a quality product, then the series has simply evolved to a different form and captured a new fanbase. Oh well.
The Fallout community had to endure several setups and even betrayals over the years. (Fallout Tactics, Brotherhood of Steel and so on....the franchise was being practically raped even before Bethesda came into the picture). On top of this Van Buran was very promising, and finally seemed to return to the heart of what made fallout fallout....then it was canceled. (Interplay was getting rid of all PC development).
Finally, Bethesda never made anything similar to Fallout. All their games fall into the giant sandbox with an intricate environment genre, rather than Fallout's intricately personalized and living world. Where living doesn't mean a bunch of generic - even engine generated - actions by NPCs, that's all bland and identical, but distinct individuals with their own quirks and fancies. Yep, it's a scriptfest, but Fallout simply had so much packed into it; with such an elaborate and far-reaching scenarios, that you really could make a difference.
In a recent interview I read, it was stated, that Bethesda purchased Fallout because the trends and objectives associated with the franchise actually cover up their own shortcomings.
...and for all the hype about freedom in Bethesda games, when you get down to it - and I played hundreds of hours with their titles - they're a big exploration game, with a minimal plot thrown in and powerplaying to give you a sense of achievement. Granted, you can play with it, but it's NOT a living world. I don't care about a freedom where the world doesn't react to me...your actions carry no weight. Either you fufill a mission or not. (Or you go on a rampage). The bottom line is, your actions never resulted in tangible consequences that you could identify with.
Compare this with Fallout, where you could talk, shoot or even joke your way out of a whole number of situations....and could do the good, the bad or ugly thing at the very same time. You could get married, be pornstar, settle a gangwar ect. etc.