Ok guys.

Few things. One if you don't want to worry about Grizz bearing down on you - don't go out in Grizz country. For most of us who like outdoors in those areas this is not an option.
Just be smart about things. Nothing is foolproof in outdoors but one can greatly decrease chances. Don't go alone, don't have aromatic food etc, don't hike on game trails unless hunting etc , make human noise - talk, carry bear spray - it is proven to work though again not 100 % foolproof and learn bear behavior and how to act, Stuff most of us know likely.
As far as gun I believe the question is what HANDGUN will stop and or kill a grizz threatening your life? Nothing is fool proof. Practice will help. That said the bigger and stronger the load the better obviously. Anything less than a high grain .44 mag is just going to end your life quicker by pissing off an already mad grizz if you shoot it with less than .44 and as many have you have rightly stated that in itself is definitely no guarantee. Personally I don't want to kill the magnificent beast anyway and at last resort but hey if between me and being a meal yeah I would choose .454 Ruger ( 6 shots vs 5 of taurus) and practice your ass off.
Also If you shoot it in the leg I don't care how mad and big he is it is going to either face plant or stop. It may recover & still come after you but unless you get side shot near base of skull or lucky shot to heart you going to do nothing but make him end you faster. If by chance you stop it and wound it in process for love of god please track and kill it. One it is humane thing to do and 2 a wounded grizz will be a greater danger to any other soul who comes across it before it dies. I would take .44, .454, 480, or 500 if picking handgun for backup to bearspray or rilfe. As stated before sometimes rifles are not an option due to size and weight if backpacking etc. Anything less as i said will only tick the beast off unless you are lottery lucky. Peace