I have no doubt they'll finish it up like they said, probably under contract to do this which doesn't change even if Amazon owns them now. Until this game is done though I don't expect to hear about the new team that will be taking over, so we'll have to wait.
Surely MS is going to try and poach some people from Double Helix since they have so much experience with the engine, etc behind the scenes. They put together a strong group of fighting game vets. If MS doesn't then I hope they have been using the time to build up their own team of vets.