Each captain has a mana pool with = the amount of soldiers in that battalion, if a captain has 3/4 mana, that means that (including himself) there are 3 of the total troops available in the unit.
When the captain dies, it resurrects it and swaps it with another random squad member and kills the replacing unit
The issue currently is that the soldiers of the squad (not including captain) dont spawn when the squad is created via training captain, or when the captain is pre-placed map start.