Clean it up. See if it shifts through all the gears. Learn how to adjust the rear-derailleur (RD). If it works - Ride On!

I doubt it's a Blaze on an old Bianchi. May be a VGt, or even a Cyclone. Those can last a very long time. Clean the bike. Perhaps an overhaul. At least a tune-up. If the RD is shot - fear not. Another RD is easily available.

Got pictures?