Just to give you some basis for judging this answer: I've been an academic mathematician for a little more than ten years, and my direct experience is with tier I research universities.
Now for my advice (for what it's worth):
Although there are probably counterexamples, my feeling is that once you leave academia, it is rather difficult to reenter. For example, it is difficult to keep up with current research if you are not in an environment where there are seminars and colloquia, and where you have access to MathSciNet, journals, and so on. Also, building a teaching resume is also an important part of pursuing an academic career, and you can't do this (at least in any conventional way) outside of academia. (There are exceptions to this --- in the old days there
was Bell, later ATT, labs, but I'm not sure it exists anymore; the modern counterpart is Microsoft Research, and perhaps Google's research division --- but I presume that is not the kind of company job your friend is considering.)
Realistically, it is also probably not easy to move from a teaching position at a tier 3 college to a more research-oriented position at a research university. But it does seem realistic (at least to me) to use this position as a basis for establishing a teaching-oriented academic career, and such a career does offer opportunities for pursuing research as well (although obviously not in the same focussed way that a career at a more research-oriented institution would). So your friend's decision should probably be based to a large extent on whether they would be happy to have a career in academia whose primary focus is teaching.