You are unable to add Former students to a new Static group once Off Rolled in the ScholarPack system.
But, if you wish to create this group for Assessment purposes, then Yes you can.
Go to Reporting>Assessment>Checkpoints Report
After creating your report using the information you have, (ticking the Include Former Students area - 
you are able to create your static group using the 'Make Static Group Filter' Name and save the group.
Please be aware though, that this is a Static Group and only shows you the information you want at this time only - this can be changeable.