One day, we'll need to handle user deletions - clearing up their game state, statistics, etc. However, it's not that easy: we'd also have to handle switching in-progress interactions to an AI - if a deleted user has 15 battles going with other people, all 15 of those battles would fail to finish (due to the deleted user being flagged as interactive, but never responding). We could switch those interactions off to an AI user or, in some cases, let the natural expiration occur (if a battle expires in 60 days, then a deleted user's shared battles would eventually be expire... but we'd have to ensure that the "winner" is the remaining user, not the user who made the last turn).

Something we can worry about later.