Sacrificial Breakthrough?

In the final round of the Spokane Falls Open, I was paired against an underrated child. Alex has been one of the strongest local scholastic players through the past two years, winning or finishing near the top of the K-12 section in nearly every event through third and fourth grade. This summer, he spent two weeks at a premier youth chess camp in California. It had a dramatic effect on his play! Now, he will be finishing near the top of our local open events. His rating going into the weekend's event was mid-1200s. (Edit: now that the event is rated, we know that he gained over 250 Elo, rising to 1515--still grossly underrated.)

I was strategically lost after a few moves, but my young opponent could not find the knockout blow. Rather, we reached a minor piece ending in which my two knights may have offered better chances than his knight and bishop. After I turned down his offer of a draw, he built a fortress.

Black to move

I spent about six minutes in this position contemplating 43...Nxa3. Would a sacrifice of a knight for two pawns destroy my opponent's fortress and give me the edge. I was not certain and opted for 43...Nb2 instead.

I let this knight become trapped in order to liquidate White's kingside pawns. After trading my other knight for his knight and removing his last pawn except for the useless a-pawn (the bishop operates on the wrong color squares), we agreed to a draw.