The thing is the deals are a revenue sharing deal - Google gives 1/3 of the revenue to Apple. With microsoft, the number could be 100% and would still not reach a significant number for Apple. Mozilla would jump at it, and I hope Google still invests in them as part of a grant or something while not getting anything in return.
Longer term, yeah they'll probably just make their own search engine.
I highly doubt Google would give Mozilla anything. The only reason I think they would would be to appease Chrome monopoly concerns, but I don't think Chrome is even at risk of that. It's not the default browser on any platform other than ChromeOS and some Android devices.