What Happens To Your Rating When Your Opponent Says "No Mas"?

[Cindysphinx]

A friend on another team asked me a question, and I didn't know the answer.

We have 90-minute timed matches. Teammate was playing No. 2 singles. Close and time-consuming first set, with teammate winning 7-5. Players started the second set with time running low. Teammate took a 3-0 lead in the second set, with time remaining on the clock.

Opponent comes to the net to shake hands and says (correctly) that she is now so far behind that she cannot possibly win so they might as well stop. Under our rules for incomplete matches, teammate would be awarded the second set by virtue of being ahead by 2 or more games. For opponent to win at this point, she would have had to reel off at least 5 straight games, which she could not possibly do in the time remaining.

Teammate wasn't sure what to do. Her main concern was that she would want this win to count toward her rating. She told the other player they had to keep playing anyway until time was used up. They did, and opponent won that final game.

Had the teammate stopped playing, would this be considered a "retirement?" If so, would the computer consider it as much of a win as a completed match?

Ordinarily, if your opponent wished to surrender, you'd happily shake hands and take the win. Teammate is wondering whether she did the right thing in insisting that they keep playing, and she is unsure whether a "retirement" can be for reasons other than injury, etc.