"Any user may make an Escrovery challenge to recover any account by first placing an amount of money in escrow. If the original account owner responds to the challenge in a certain amount of time, they earn the escrow. Otherwise, the challenger takes ownership of the account and recovers their escrow."

Are you thinking the response has to be the same amount? What if challenger puts down $1M - do I have to match the amount? Or will $1 work?

What would the time period be? What if I miss the notification or the email?

With some refinement and supporting systems, maybe this could work for some economies.