I bought a chilller to use for the first time today. While the wort was chilling I walked inside and when I returned a few minutes later the pot was overflowing. One of the plastic connections came loose and filled the pot with water. I sadly tossed the brew. There was no saving that beer was there?
If you thought that the overflow had just started, you'd still have all of the flavor in the wort in your pot but just watered down. If you had 5 gallons of wort in a 6-gallon pot, re-boiling for an hour or so to get rid of the one gallon of excess water might have worked. If you had 2 gallons to boil off, it's not worth it. I think you did the right thing dumping the batch. At least you still have yeast to use for another effort.