Authorisation of ArcGIS 10 desktop outside maintenance period

Hi

We have a number of single use desktop licenses which have been in maintenance for several years. A few of these are sitting at 9.3 and though we have received the upgrades we are eligible for, we have not yet applied them. My organisation are now considering dropping maintenance on a few to save money. Someone has suggested to us that if we do drop maintenance, we will be unable to apply the upgrades we have already received during the maintenance period. Is this correct? I fully understand that I will not receive any further upgrades but surely the upgrades we have already received are ours? When you buy a licence, it is a perpetual licence - even when you drop maintenance. Can anyone advise? Thanks