Whether, like Colin, in retrospect Willie Lee and Baptist would feel that what has vanished was greater than what was achieved, is not something we can predict.
When you consider something in retrospect, you think about it afterwards, and often have a different opinion about it from the one that you had at the time. In retrospect, I wish that I had thought about alternative courses of action. in retrospect thinking back to a time in the past, especially with the advantage of knowing more now than you did then (retro- + -spect (as in prospect))