It would be useful to have versions saved in Project Online for the schedules. Since the emphasis is brought on the web access and the focus is on the ease of use, having versions of the schedules would be great. It could be configured (number of retentions) in the PWA server settings, like it can be done on Sharepoint lists. And the restore should be as easy as selecting a version, viewing it and restoring it.
This can be merged with the following feedback:
Dear microsft, it's good to have this functionality as customers are expecting for the schedule versioning in project online.