Rollback blocked by schema mismatch

v300 of the user service deployed at 11:00 with a migration that renamed the column 'phone' to 'phone_number' and the app now writes to 'phone_number'. At 11:20 you discover v300 has a separate bug corrupting notification preferences and you decide to roll back to v299. But v299's code reads/writes 'phone' which no longer exists, so a naive rollback will 500 on every request. Meanwhile 20 minutes of writes have only landed in 'phone_number'. Walk me through how you safely get back to a healthy state.