Can a worker leave a territory controlled by an enemy mech?
No. The worker cannot leave a territory controlled by an enemy Mech. The rulebook says:

If your character or mech move into a territory
controlled by an opponent’s character and/or mechs,
its movement ends (even if you have a mech ability
that would allow it to move further). The opponent
still temporarily controls that territory. After you’ve
completed all Move actions, if any of your mechs or
your character share a territory with an opponent’s
character or mechs, combat happens (see Combat
section, pages 22-23).


Your workers cannot move by themselves into or out
of territories controlled by opponent characters and/
or mechs.