Indeed, not the result you hoped for but you did see this through to conclusion... None of us are perfect and many things are outside of our control. There is a delicate balance at times of when to pursue an animal and ultimately we have to use our best judgement with the resources, knowledge, experience, and time we have...
There are no guarantees that waiting longer on the initial pursuit wouldn't have ended up with similar outcome considering the predators in the area. I commend you for using a "string tracker" in that kind of watery swamp area. Very tricky to trail in that environment.
We've all had tough decisions like this to make, and sometimes the outcome is not as we'd prefer. Apart from sleeping in the woods at the last known blood/bump for hours on end waiting for morning or the yipping of predators this will always be a possibility. Except for perfect shots, perfect blood trails, deer always falling in sight, etc., etc... Back to the No One OR life not being perfect.........
Hold your head-up, learn what you can to make future decisions the best they can be, and appreciate the blessing of the encounter and finding the animal/closure. That's a great buck and looking forward to the rest of the story!