I'm getting old enough that such questions are in my future planning. A time will come when I cannot go shoot, or shoot well, or shoot some things, and stuff the kids don't want or I need to pay bills will get sold off slowly.
So, what is the last one if it got to that? Depends how old and broken I am which gun I can shoot well. I don't use revolvers much now, but can easily imagine, for example, that the last one in the model 19 as I can run it with low-recoil loads. So while today it might not be the last one I'd keep, in future that will likely change.
I empathize. By age fifty, in late 2011, .40 S&W, fired from the high-bore-axis SIG P229, was becoming a problem. I sold or traded-away four .40 SIGs, just keeping one, because I still had to carry a .40 duty pistol. Thankfully, in 2015, my chief finally OK’ed 9mm to again be an alternative duty pistols cartridge, as a step to making 9mm the standard duty cartridge, a year or two later, relegating .40 to alternate status. (.45 ACP was already an alternate duty cartridge.)
By age 56, in late 2017, some 9mm auto-pistols were starting to become a problem. Firing a mere 80 rounds, right-handed, during a duty pistol qual, with my two Glock G19 pistols, caused pain and swelling that lasted two weeks. (40 rounds right-handed, and 10 rounds right-handed, per pistol.) Thankfully, after two weeks of healing, I fired quals with my larger G17 pistols, and 1911 .45 pistols, with no swelling or pain afterward.
Eventually, I determined that a handgun’s grip needed to extend far enough to brace firmly against the “heel bone” of my gimpier right hand, if shooting 9mm/.38 Special, or anything more powerful than those cartridges. I put my G19 pistols in the safe. I then traded them away, in 2020, which was a good time to get a good value for one’s trades. So, handguns with duty-sized grips are now my right hand’s friends. My smaller-gripped guns, if more powerful than about .32 ACP/H&R, are now relegated to left-hand shooting. Notably, a Ruger SP101 has a grip that is just long enough to brace against my hand’s “heel bones.”
As for Magnum-level ammo, I only shoot full-pressure mags with my bigger revolvers, in quite small quantity, and mostly left-handed. Fortunately, I am functionally ambidextrous with most of my handguns, especially the DA revolvers. (I write lefty, so pulling a trigger lefty has never been a problem. I chose to carry on the right side largely because I throw right-handed, and use many heavier tools right-handed, so, drawing the then-mandated heavy duty revolvers, from the then-mandated low-slung duty holster, back in the Eighties, felt natural when done right-handed.
I should add the disclaimer that we all have uniquely personal hands, and that the multiple things wrong with my right hand are not necessarily the same as anyone else’s, so, my solutions will not, necessarily apply to anyone else.