Engineer at PlanetScale here: it _does_ work if data has been written to the new structure!
In your scenario, you drop a column, populate some new rows in the new structure. Then, you regret the migration and rewind. You get the column back with all the pre-dropped values, AND you get to keep all the new rows which you've inserted.
The values for the now-restored column for the newly inserted rows is the DEFAULT value per column definition.
In your scenario, you drop a column, populate some new rows in the new structure. Then, you regret the migration and rewind. You get the column back with all the pre-dropped values, AND you get to keep all the new rows which you've inserted.
The values for the now-restored column for the newly inserted rows is the DEFAULT value per column definition.