They certainly did make flattops earlier. I used to have a 1928 Gibson LO flat top--little black job. Punchy sound.
Poor condition meaning what? Does he know anything about guitars? I doubt he does if he thinks he "can't get strings for it". Of course he can. Way better ones than were ever on it before.
A 12 that's been strung but ignored for that long may have trashed the neck by now. But if it was tuned to C, I think there's hope, since that's really low-tension.
No doubt he could spend a lot of money on it. There's no way we can guess whether it would be a worthwhile investment, since even you haven't seen it. Take it to a repair shop, preferably a vintage specialist (meaning more generally, a highly-experienced-with acoustic guitars repairperson.)
If you tell us your general location, I'm sure we can recommend someone.