Customers leave when prices rise above their willingness to pay. Some customers will realize on their own that they can bypass Apple's fee by subscribing through the browser, but most won't (since Apple forbids even mentioning this trick).
Only if the users follow. If users decide they won't use the mobile web then patreon and the creators they represent lose. Nobody knows for sure, but there is a general belief that users will not follow (or at least enough won't follow).
Perhaps, although that requires experimenting the new fee model first.
It's too big of a decision to take without actual numbers, and having gone through it for a few months also helps on the communication side: on the surface Patreon at least gave it a try, and there's even a chance users are pissed off enough by the new model to campaign for that change and defend the move to their fans.
