If my opponent used the list on my unit for -2 might, i trigger temporal breach, does that unit come back with -2 might?

No — the unit comes back at full Might.

Banishment is a Non-Board Zone, and Rule 124.1 says any object that changes zones to or from a Non-Board Zone becomes a new object for tracking, wiping all temporary modifications (damage, counters, statuses, layer alterations). The List's -2 [M] is exactly that — a temporary "this turn" modifier on the old object, so it's gone when Temporal Breach replays the unit as a fresh object (Rule 124, 427). The unit re-enters with its printed Might and would need a fresh -2 to be weakened again.