Guess you have to look at your situtation/location and think about your needs. If you feel that the mauser will get the job done and you are purty salty with it then all is well. My frame of mind is when i grab a rifle, the threat is out of the range of the shotgun. Distance for me translates into time and stay behind cover. And the greater the distance, especially on a moving "target", the more difficult the shot.(another reason i'm a fan of the shotgun).
The sks or any semi-auto means a fast repeat shot if necessary and faster engagement on multiple targets. For myself, i do not posess the necessary skills for fast repeat accurate fire with a bolt action as i have not practiced doing it. But again, i consider the distance to be to my advantage to do what i do best with a scoped rifle. I have tremondous respect for the sks and consider it a bargin for someone on a budget. The sks is a big improvement over any handgun round in ballistics and recoils much less than an 8mm mauser which helps out further with fast repeat/accurate fire.
The hi-point carbines are interesting in that one wonders how something so inexpensively made with plastic works so well. As much as i would like to bad-mouth the guns, they seem to work quite well. We have a deputy that has a 9mm carbine and head shots are no problem for him at 50 yards on a b-27 target. This may be a good route to go if you want ammo compatability with your handgun. This ought to carry real easy also in your vehicle should you want to keep your SHTF weapons close at hand when working or on the road. Another possible option but more money is the kel-tec 2000. Available to order to accept glock, sig, smith, or beretta mags, this little booger is light and folds in-two. Only thing i know about them is what i have read and most of it seems positive. Some folks have posted elsewhere that they fold them to easily carry on their motorcyles when traveling---they just saddlebag it or put it in a small case.
Its just gonna come down to what your comfortable with and how much you want to spend......
You know your abilities with what you already have on hand. If you see a "hole" in the line-up, then pick what your comfortable with to fill it.