When I was buying rebuildable salvage titled cars, my max was typically 1/3 of clean value. Clean title would be worth a bit more especially if was still under warranty. For me disassembled cars were less value, because nickels and dimes add up. Cars with in demand drivetrains (Mustang 5.0's, Camaros, CTSV...) were worth the value of the drivetrain.
Seems that most clean 50,000 mile 2018 Impreza's are listed for $16,000-$17,000US. I'd think as a private sale repairable, it'd sell for about $3,500US. He's in a major metro area. I'd bet he'll find a buyer.