Seems like this should have been one of the first thoughts....You can't get coins back from a wallet, nor can you stop that wallet from spending...considering he/she/them is the creator of the coin, they would retain the rights...so as you build up this 'new' coin, you are essentially giving this old dev 30% of the available coins. I'm not sure how you can stop this from happening...a new coin should have been made and then offer exchanges.
To solve "the problem" with original dev is one of our top priorities, and we are very confident we will solve it in a very sophisticated way. If you believe in us and support us, we appreciate it, if you don't than I wish you all the best with your project.
Cheers