You're relying on the fork to remain maintained, or else you risk you run into build/functional issues at some undetermined point in the future when it becomes incompatible with other changes in your environment/project. If you don't trust the fork will be maintained, you should begin decoupling your project from the library anyway. I would be more willing to trust an alternate (or no) mocking framework over a Moq fork to be supported in the long term. That might change in a couple months if one becomes established.

I would personally wait a couple months, or until the original Moq creator reverses course. (If he does that, I think it's unlikely a fork will compete with the original, so I'd start removing the dependency as I can't trust the author anymore.)