At an implementation level, you could make it optional for customers to delete their data (preferably opt-out of deletion). A purchaser looking to woo your cli

At an implementation level, you could make it optional for customers to delete their data (preferably opt-out of deletion). A purchaser looking to woo your clients (and continue to provide your service) rather than exploit your goodwill shouldn't have trouble retaining the majority of the data. There's no reason to force data deletion, but leaving the choice to customers if they want to trust the purchasing company the way they trusted you prevents a lot of conflicts of interest and abusive behaviors.