An SRM failback is essentially the same process as a recovery, just instead of site A to site B, it is site B to site A. So all comments mentioned in the recovery section apply. The only main difference of a failback from a recovery is in that a failback implies that there was at least once recovery from the opposite site already executed.
To the end user this doesn't really change anything and how the process is managed or reflected in SRM or in vSphere. With that being said, the FlashArray SRA will attempt to re-use the original volumes, if they are still there. The SRA looks for volumes with the name of the volumes to be failed over with a suffix of -puresra-demoted. If the volume has been renamed or of course destroyed, it will not be re-used and the SRA will create a new volume with the correct name.