It is usually 5 to 7 years from product cancellation, but they already cancelled and no longer provide depot services for the "A" model MT1500 and XTS2500 series that have the 4 meg controllers so YMMV.
Rebanding is also still occurring in border states and the agreement with Sprint/NEXTEL are analog versions of these radios that are similar to the MTS and LCS radios so if they are still providing RB radios then warranty services will still have to be provided.
Also I believe a lot has to do with how flooded the market is as they supported the MTS/MCS for almost a decade after they were initially cancelled. Rebanding flooded the market with XTS2500 and XTL2500 radios and a lot are still new (under 5 year) deployments.