After reading all this, both sides are to be blamed here.
Interplay:
Interplay was in financial trouble(why?) but if any company is in financial trouble, the last thing you would want is to sell off your most popular franchise. I would rather go down and fight it off till I can't do it anymore. Also, you would think they would do anything to keep the original team (now at Obsidian I believe) and let them be a big part of the company.
Another thing is the deal. It's very clear what Interplay was trying to do: Give fallout to Bethesda,let them work on it, and whatever ideas they use on that they will "leech" off it and use it on their MMO. It was a dumb strategy, and no company will fall for it. I read that after Beth told them they can only use the name "fallout" and nothing else, everything stopped. You would think Interplay would clear all this before they sign something like this.
Bethesda:
Bethesda is obviously trying to stop them from making this. They want to be main company, not Interplay. It's greed, and nothing else. Then again, they created the content, vault-boy, the gameplay, the mechanics, the world, etc. They marketed this game and brought it back. They can't just let Interplay take everything away like that.
Regards to the deal, Bethesda should have atleast given Interplay a second chance on it. But obviously they didn't(since they follow the contract too much). The lawsuit was expected since (again) they followed the contract terms, but Interplay obviously needed more time then that. They did not have the funds, and no way they were gonna get it in time.
In the end, Interplay and Bethesda should have just worked together(like ID,arkane,etc.). It would have benefited both, and none of this would have happened. I know Interplay was in trouble, but you would try to make sure you do everything right when you sign a contract like this. Interplay should have walked away if they didn't get the terms said out aloud by both parties.