Just some thoughts to consider:
An AK pistol is a ludicrous idea.
Hard to hit with on moving targets to begin with & damned near impossible with one hand in a hurry if needed, not to mention the difficulty of on-body carry.
Shotguns are not in the running as backups to a hunting rifle.
Regardless of effectiveness with slugs, nobody's going to carry two long guns.
The huge Smiths in .460 & .500 are extremely ungainly & heavy, and followup shots would be difficult in short time frames.
I HAVE fired a .460 Smith one-handed & it can be done, but not recommended.
The Taurus combo gun is large & ungainly, no real point in its supposed versatility when the goal is a totable backup sidearm for bear.
The idea of a backup handgun is just that- a backup.
It's always on-body, and that means at times when you set the rifle against a tree to cook, process meat, or do what the bears themselves do in the woods.
You won't always have the rifle on you, and a handgun may be quicker to get into action along with offering faster follow-up shots if needed & time allows.
The handgun can be fired one-handed, if the off hand is injured or circumstances indicate & require it.
Rifles are more difficult to both operate and fire with one hand.
I would personally find a revolver more emotionally comforting than a semi-auto, in such circumstances, but that's just me.
The .454 can be intimidating & not really necessary in the Wyoming bear habitat, in my opinion.
A GOOD .44 Mag with the RIGHT bullet can handle the job, and with much less fuss than the .454.
A light-framed revolver is easier to carry, but offers more recoil, and may affect your ability to shoot it well.
A heavier revolver will handle recoil better, be less intimidating if you don't shoot enough to get used to heavy recoil.
A well-constructed chest rig or shoulder rig easily & comfortably carries even a large 6-inch or 7.5-inch all-steel revolver above the belt, where it's easier on your back, and won't pull your pants down.
Access is also excellent, IF you wear such a rig outside your outer layer of clothing.
Wearing a long coat over your gunbelt may slow down access to a belt-carried gun.
Any carry inside multiple layers of clothing in a concealed-carry type holster denies quick access.
And finally, to answer the "What do you carry..." question- In the mountains of Idaho I carried a 4-inch Ruger Redhawk with heavy Garrett .44 Mag solids.
Nowdays, I may alternate between that or a lighter Smith 629-3 in .44 Mag, again with an appropriate non-expanding bullet, in the Utah mountains.
Both are worn in Galco chest or shoulder rigs, depending on season & mood.
I also have a De Santis chest harness for a 6.5-inch Ruger .44 Mag Blackhawk, but generally prefer a DA revolver.
For lighter work, I may take a 4.2-inch Ruger SP in .357 Mag riding in a quick on/quick off El Paso Saddlery Tanker chest rig & loaded with Buff Bore 180-grain lead semi-wads.
Such "high-carry" leather keeps weight off my belt, immediately accessible over outer clothing & in any sitting position, and doesn't situate the handgun where a hammer will tear up a rifle stock if slung for long periods on foot.
The Desert Eagle in .44 is a big & heavy gun, and in .50 you will NOT like the recoil.
Again, just some thoughts to consider.
Denis