So you know, https://enty.jp/ is largely this. Some of the creators I follow there are moving to Patreon though, interestingly.
The Japanese creators I see (mostly visual artists) also don't seem like super huge fans of the idea of digital content, which is what Western folks on Patreon largely expect. Japanese creators seem to like selling books and such at conventions and rarely sell their books digitally, which is a bummer for someone who doesn't want to pay international postage. I have seen some change this though (the ones who moved to Patreon).
You'll probably lose some portion of your income due to the friction, but given that your patrons are likely to be fairly devoted fans, I'd imagine the retention will probably be pretty good.
For now you sue them.
If they get large enough and it happens often enough some form of regulation will likely be enacted.
That's no different from your employer shutting down, it happens, people move on.
That said, patreon is centralised. What happens if you're a creator and that $2000 a month stops coming from patreon? I trust and believe in the now, but who knows where they'll be 5 or 10 years.
PS. Patreon, please make a Japanese version of your site!