Seems like a good idea. I can't believe that they currently give two and a half minutes. I think the length of time depends on the time control.

So it seems like they already have an evaluation in place for a disconnect while losing. Seems like it shouldn't be that hard to add a disconnect while good case.
Maybe you could submit it as a suggestion.
Feature Proposal: Disconnect Buffer for Winning Positions
Problem:
Currently, Chess.com gives disconnected players 2 minutes 30 seconds to reconnect. While this prevents abuse, it unfairly punishes players who are clearly winning but suffer an unavoidable internet hiccup. Losing a completely winning game this way feels worse than any blunder.
Proposed Solution:
Introduce a hidden reconnect buffer for players in winning positions.
Why This Works:
As an example:
In a recent game I played, I was completely winning (up a full rook and pawn w/ eval at +5) when my connection briefly dropped. Despite having a decisive position, I was flagged as lost after 2 minutes and 30 seconds. A hidden reconnect buffer in such cases would have preserved the fairness of the result without affecting my opponent’s experience.
Of course, as any other player I thought that it would just be a small WiFi hiccup that would only last 30 seconds up to 1 minute. But after seeing it's still not reconnected, and that the WiFi logo on my phone had an exclamation mark (!) next to it, I immediately went to turn it off and on again asap. But unfortunately, I had to wait for a whole minute for it to come back, being delayed by 5 seconds after the reconnect timer went to 0.