If it's a pre 9.1 system with ADI licenses, there is no way to get them back and they are screwed, they'll need to buy equivalent PLDS licenses.
If they had PLDS licenses (Licenses section shows PLDS Host ID), then you can use the CAT tool to take over their licenses in PLDS and view/download them from there.
If you don't have a PLDS login, consult with a local Avaya Partner.
Cheers,
BFG9K
Avaya IPO/ACCS Technician
Melbourne, Australia