Stress is an interesting element of the game, but it needs to be a combination of a number of factors, i.e.(Bravery, Reflexes, and Hit points), and recovery should also be link to the same. This is so that you will have more unique characters in the game, and give your a better dynamic's experience, within the game.
At the moment you know that a character will be out of the game, after 4 missions, which means you need to hire more troops, so you have to build more barracks, and this takes up space in the base complex, which reduces what else to can build, later in the game, and at this time in the game, you have a finite number of base squares to build in. Then you need more power??