I don't have that much direct experience with actual fistfighting, but from very careful study of real-life examples and mildly dramatized examples, I can assert a 'realistic' fight between any two of the Skullgirls' cast would last about 1-2 seconds before the victor would be made apparent. Take a look at this footage of a fumbled robbery, and try to time how long the 'fight' lasted for:
The fact that over the years Annie managed to kill countless Skullgirls but not Double suggests that the latter is either more powerful than a Skullgirl or harder to wipe out at the very least. That being said, I doubt what happened to Double at the end of Squigly's story was more than a temporary setback.