I'd keep it. Solid comfortable ride, bulletproof frame even if it is heavy.
eBay always has parts for old Schwinns. Dang near any derailleurs from 1960s through 1980s should work on your bike. There's an online store called schwinnstore run by Craig Morrow. He usually has auctions going too. If you buy anything from him, tell him "The Bicycling Guitarist" sent you!
I like the SunTour V-GT Luxe rear derailleur a LOT. It came stock on my
1977 Sportabout (a poor man's Varsity) but was a superior design to the French-made derailleurs of contemporary higher-priced Schwinns.