Sorry for the pedantry, but you're confused. Mr. Fusion had little to do with time travel: it was a commercial device which Doc got in the future, and which simply generated power from whatever you wanted to pour into it. Doc's flux capacitor is what allowed time-travel, and it needed a lot of power. So before, he had to either use uranium or lightning, but after installing Mr. Fusion he didn't need either of those hard-to-get things.

So, if Mr. Fusion was a Google product, as soon as McFly transported the DeLorean to the future (outside Google's window of support) and the onboard computer synced the time over-the-air and the Mr. Fusion updated its clock, McFly would be stuck in the future, though presumably in that time he should be able to find some competitor to Mr. Fusion which he could replace it with (with Doc's help; McFly never seemed to be very good with technical things).

TIL, turn off autoupdates and clock sync when doing any sort of time traveling.

I was simply remembering the end of the first movie where Doc drops a beer can, a banana peel and so on into the Mr. Fusion so he can take Marty and his girlfriend into the future and joking when Doc ended up in 198-whatever Mr. Fusion would refuse to work because it was out of support. I think you're interleaving the timelines of later movies?