The only 'obligation' he has is to honor Patreon's terms, as that's the framework of any financial support he receives. And we've talked about that in this thread at length - those terms do not 'obligate' him to deliver any content at all, let alone finish anything. He is not beholden to a production schedule or timeline.
When you back someone on Patreon, you are supporting their talent and their ideas. Not their output. That support brings certain perks (wallpapers, early access, etc), but it doesn't assure new content.
His Patreon supporters either understand this in a way the whingers around here do not, or they simply don't care (either from apathy or ignorance). Either way, it's their money to part with as they please.