From T328032#8936008:

Additionally, we decided that if a participant registers for an event, answers questions, and then cancels their registration before the answers are aggregated, we will also delete their answers (and pretend that they never answered in the first place, in case they choose to register again later). This is based on the assumption that we won't keep data without a valid reason to do it.

This task is about implementing this in the code. Details TBD.