IDK... that's a difficult call. The GM, like everyone else, has a life, so respecting that is first priority here. Second, this is their story, their original concept, I would hate to confiscate it just because of their lack of attendance and management of their thread. I just want to give the GM all the time they need, but that jeopardizes the interest here....
First, let's just see who else is here watching; see if the interest is still here.
Then, give them more time to, at least, respond; to inform that all is well and they haven't forgotten their thread.
If they don't return, I suggest that we don't take anything from this thread to create a new, or even begin the RP without them. Instead, I suggest someone building a simple RP of a similar nature that our charries can work well within, and we run that. If the GM returns to this RP, then great - we just hop right on in and start. If not, then our charries were not created in vain; they'll have a story to live within, and possibly, another nice story comes of it all.