Okay, I'll explain. In my own case, a temp worker coming in would be all but worthless. To replace my current primary employee in one of my businesses—whether permanently or for a year—would take me 9-12 months of daily training. Since I own other business interests I have to take care of, this means that something would definitely have to suffer. It's definitely not a matter of just "hiring someone to fill in." Utterly impossible. And no one worth hiring is going to take the job anyway with the understanding that they're gone as soon as someone else gets back home. I don't mean it sarcastically in the least when I say that you fail to see how it's a hardship because you're not the one trying to make it work. Thankfully it's not an issue in any of my present circumstances, but holding a job for someone, no matter how noble the reason, would be a practical impossibility.
MM
Not impossible, in fact it would work great for a national chain. You move an trusted area assistant manager(s) into the position temporarily. The position is filed and the chain can "test drive" these assistants to see how well they'll get along in the position and whether they can move up someday. It's the same as running a school for managers, and they'll have a pool of qualified assistants.