I think it depends on if you're the dumper or the dumpee.
I left my ex-husband and got over him immediately. It took a week or two for the shock of having left to subside, but I can't say that I ever looked back or navel gazed after leaving him. I was simply having fun getting out and doing what I wanted. And it was fun to be dating again too.
However, if I were the dumpee and didn't want to end things, I can't imagine that it would be near so easy.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.