If ext4 was proper from the start and did not truncate some opened files after crash, the amount of lost data would be limited to that written since last flush (say, 30 seconds) and thats it. Thats better than backups can do in this case.
Backups will never be able to completely prevent data loss. They are mainly to prevent a complete disaster in case of hardware failure or gross human error.
In day-to day work with experimental drivers, you should be able to trust your file system to prevent any 'appreciable' amount data from being lost. Thats the ideal we should strive to.