AoT will have system of medical lines to extract the wounded out of combat and first line. Harder the injury, harder is to give injured adequate medical attention.
Use field medical units and field hospitals to help injured and bring back lighter wounded soldiers to be ready again for the combat.
On the end of each mission there is report on casualties. Beside dead, injured soldiers could be brought back to the battles during that battle after some number of turns, or to be prepared for next one. Harder wounded will be send to further hospitalization and brought back in some future mission.
Old soldiers that come back from hospitals will preserve own experience. If player doesn’t pay attention on medical issues, then soldiers that died have to be replace with completely new soldiers which are inexperienced and that affects unit in total.
Also, new soldiers cost prestige, the main players resource for building up his own army. Save your soldiers, tend the wounded and you ll have more for new units and new equipment.