I'd wager it would still last another decade or three.
Well that's good news. Once I'm done with the wife's '76 Raleigh, I'm going back to it and finish.
I've done a fair amount of brazing in my day job, nothing related to bike frames. I'm kicking around the idea of brazing reinforcing saddles (1/2 or 1/4 rounds of tubing) over the affected areas with heat blocking paste and wet rags to control heat spread. Good idea or not? It's so close to the bottom bracket, maybe not.