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If they pull it from the store (and their account isn't terminated), it just stays in your account for you to re-download.

Some developers will pass ownership to another one, some won't.
 
It is not always simple to get into the code of somebody else, and I think this counts double for the app store. This is because most people tend to develop something that interests them first.

The second app you posted was updated in October, it seems a bit odd to call it 'dead', it might be that the dev does not have the iPhone 7+ and can not test it reliably.
 
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