No, it will not lose its programming. But if power is lost to the T-Max (battery disconnected, ECM fuse pulled, main fuse pulled), it will not recognize the sensor settings on the bike. The program will be intact. So if you lose power to the T-Max, you should cycle the power 30 seconds on, then 30 off, and repeat for 3 full cycles. This allows the T-Max to reacquaint itself with all the sensors on the bike again. The install instructions come with a sticker to be placed next to the battery with this info on it. This must be what the mechanic was thinking of.
2005 FLTRI Black Cherry, 95" Big Bore, Thundermax w/Auto Tune, V&H Dresser Duals w/Klock Werks SS, Andrews 26 Cams, SE Stage 1 intake, SE OD/6 Speed, Wards FCS cooling fans, Krome Werks Stretch Heritage +2 bars, Progressive Monotubes, 444's, & Touring Link, Michelin Commander II's, 14.5" Madstad, Lowers with Classic Motorcycle Vents, detachable King Tour Pack, Daymakers