It would be great if any/all of these developers/companies can guarantee the app will be around for X days / years after the user buys it. Then it's a contract and you wont feel bad/betrayed once the app is gone (acquisition/bankrupt etc)

They can always end of life it after their last sale.

This guarantees the user that it's worth the time/investment, and the company can always decide to prolong the contract / expiration date.

Software (Best if used by X/XX/XXXX)