If the ball leaves the free blocking zone (a handoff 5 yds deep) and then re-enters the free blocking zone (the runner runs up the middle) do the rules of the free blocking zone still apply, or do those rules stop once the ball leaves the free blocking zone, regardless of the ball going back into the free blocking zone?

I really don't know anything about the rule, other than what I've read on page 5 of the 2002 "Simplified and Illustrated".

Those rules stop once the ball leaves the free blocking zone, regardless of the ball going back into the free blocking zone.

The free blocking zone disintegrates once the ball leaves the zone, therefore, the scenario you describe, that is, the ball re-entering the zone, by rule cannot occur.

Free blocking zone exists while the ball remains in the zone.
 

Ed and BBR are correct. Once the ball leaves the zone, the zone cannot be re-established during the down.

A few years ago the NF had a requirement that blocks below the waist had to take place on the initial charge but this requirement was removed a few years ago.