I have a halloween hermit, pretty cool to look at. He came with a bunch of red hermits I bought. He lived with my first fighting conch for a year or so just fine. He was also did not change shells for a long time. After I upgraded my tank, the fighting conch died, I assumed of natural causes. I should add, not only are these conches neat, but they are useful and not very cheap. The halloween hermit started wearing the conch shell, it took him almost a month to be strong enough to get off the sand bed with that beast of a shell on his back (lol). Six months after the upgrade, as the algae started to form, I felt it was a good time to get another conch. He did not last more than a month before the halloween hermit killed him off. The hermit wore the shell for a few days, then switched back to the other one. Last weekend the hermit put the new conch shell on, then switched back after a couple days... It is like a weekend party hat for the guy now...
Long story short, either keep lots of shells on hand, or expect your hermits to kill for their new home...