The only way I could see them doing it in a few weeks is swapping it out with something with a very similar api like inferno or preact.

Apparently the Gutenberg Element concept (https://github.com/WordPress/gutenberg/tree/master/element) wraps React to minimize contact with React itself. So converting to Preact might not take over long. Note that I haven't dug very far into the Gutenberg codebase so at the moment I am just supposing.

Yah I LOL'd out that one. A year from now we'll be reading the postmortem of the problems the Gutenberg team has faced swapping out React for another library and how things still aren't quite what they used to be.

Depends on how it's written. I'd suspect they've done a pretty good job on eeping the engine as decoupled from their code as possible. It'd probably be just a matter of rewriting a translation layer.