If Bolt did all his prep and then gave it his all then I doubt this will trouble him. It will win him fans as we've seen him as a winner and now a good loser.
If he didn't train to his normal levels then he may be kicking himself for a while. He still went out of the sport as a world championship medalist.
Gatlin : for him personally it would have been huge. Imagine having a nemesis over a decade and finally beating him. However for must of us he's tarnished. I don't get the rules about allowing cheats back in. I know they are the rules in place but the cheating helped him up his game. In my mind he'll always be a smidge better than he would have been if always clean. As we saw it only takes a smidge of difference between winning and being third.