The deception of the question, "What if?" is that it will always work both ways--'what if I'd stayed/gone/said yes/said no'--and it will never have a satisfactory answer. So why ask?
Of course, the alter ego, knee-jerk response to this question is to project and think and worry and weigh and then think a bit more. But all we're doing is worrying away the time between our fingers until it's stretched so thin it has no hope of telling us anything.
The only choice you can make, the only answer you can give, is based in the now. How do you feel *right now?* You will never know what you might have decided tomorrow because it's impossible to be two places at once, so why try? Why sacrifice another day to 'what if?'