What happens to Reggie when Mike Bell returns?

Reggie is the 3rd down back and continued to get in as such even after the fumble.

So to answer your question, nothing will happen to him.

I don't think that it's so cut and dry my man.

Pierre has the versatility to fill in nicely on the 3rd down role, and Mike Bell is a bit more of a hoss for 1st down and 2nd and short.