A soldier that deserts from the army and is captured by the enemy should be left behind.
Nope, every soldier comes home. Period.
He can face the consequences of his actions here, in court, with a proper trial.
A soldier that deserts his post and seeks out the enemy to help him IS the enemy.
"Hey terrorists, wanna give him back? No? Ok, we tried"
No solider should ever be left behind
An effort should be made to get him back, but not an endless one.