If the franchise dies with its original owner, it won't be much of a franchise won't it?
I believe Touhou has a large enough fanbase to support itself that even without the official creator, (like Gene Roddenberry) the franchise would be taken up by those who are willing to invest and make it go on.
I won't be surprised if Tasofro decide to do it, although a variety of others will climb on ZUN's body and continue his ever growing empire.
Hey, maybe there will be even better stories, stories that make sense, humor and doesn't end with tea parties!
At least by that sense, it will actually make sense to watch a Touhou anime.