Even assuming a decent chunk of patrons are at a higher tier, Patreon and bank fees are going to cut a good chunk of it. They're probably making a decent middle-class salary out of this, but it's a temporary and highly variable salary for a project you can't really put on your resume.
That said, they don't really seem to be doing too much actual work so it's probably easy living for them right now. I'm curious to see what happens to adult game developers after their Patreon income winds down... I'm not guessing it's good.
I mean, Adult game developers that are actually treating it as a full time job probably learn enough from their time to move forward with 'real' projects. Beyond that, I would guess you just go back to whatever you were doing before hand. Even if that's bagging groceries.
I'd think, if I was doing a project like this one, and getting the level of income that this dev does, I'd be making a nest egg and actively living a bit below my means to ensure it is sizable. Then, if patreon falls through, I have funding for a trade school, or maybe even a decent start on funding a degree. Nest egg can also keep afloat for a bit while looking for normal job.
Then again, I'm a rather economically frugal person in general.