I don't want to terminate the contract, though. I'd rather just finish what we started. It just seems like he lost interest, which isn't really fair to me, right?
He could be in hospital, he could be dead.
He could just not like to work with you anymore, because he don't like you or he got a better job or he stole your idea.
If you have to finish your software, I hope you have a copy of everything you did till now and get a new, reliable, dev for that matter.
If you can wait longer and want to risk, that he hadn't had a good reason to not respond anymore, just do it.