I don't think there's a valid contract since that would have been through their previous publisher Starbreeze, but MS is smart and they have probably seen from Epic what happens when you pull a switcheroo on a crowd funded project. It's a ton of refunds and bad PR. They COULD have done it but they're smart enough to know not to.
I think late summer, sometime in August, and I base that mostly on where they are in both the production and marketing cycle. They have been content locked for months now, and they're doing a lot of press and interviews, this is coming out before their big fall titles.