Mike, there are two things that have to happen to transfer an app : (a) the app itself — we much prefer that the original owner transfer the app (because we don’t want to be in the business of verifying the situation) but if impossible, we can transfer that for you, (b) the underlying data/spreadsheets need to be transferred
Without (b), the app won’t work. So not sure what to do about it. I would recommend if possible that the person’s email be re-activated in order to make this transfer happen seamlessly. I know that if you are using a Google domain, the account may have just been suspended rather than deleted. If so, it is easy to restore the account.