If the employee leaves your company (but doesn’t retire), they can reach out firstname.lastname@example.org and request a transfer of their Group RRSP into a personal RRSP account. This would presumably happen after their last pay period, which is typically later than their last day. Once that last contribution has been made, their status on the admin dashboard should be set to archive.
If they retire, their RRSP turns into a Registered Retirement Income Fund (RRIF) that they can withdraw money from to pay for retirement (income tax would apply to any withdrawals). Again, once their last contribution has been made, their status on your admin dashboard should be set to archive.