Hero Improvement (Withdrawal)

Allow the hero to have the option to withdraw with 50% of what it takes to mobilise, as it must be on friendly territory, and it will be vulnerable during that time, and it will go into cooldown. At least this gives the option to withdraw and select new units instead of sending them to their deaths just to do it anyway, and it makes it more tactical, as withdrawing them will mean that it will take three days to call them back, as it will instead be a tactical choice and a lot of things could happen in three days where might need that hero again at that point.