"shell shocked soldier" = protagonist
"he’s wounded attempting to destroy the source of the invaders power" = inciting incident
"vengeance on the invaders" = main character goal
"saving a group of forgotten teenagers" = main character goal
"post-invasion Europe " = setting
The potential weakness, feels like it might be the double main character goals. While it is presented as a potential 'Sophie's Choice (1982)', it lacks the depth of a moral dilemma.
External conflict is great, should character do X or do Y, but it is Internal Conflict that truly tears a character apart. Internal conflict is psychological. What type of character is our shell shocked soldier? Courageous? weak? sentimental? passionate? honorable?
An honorable character might choose serving his army, over saving forgotten teenagers. But a Sentimental character might choose saving teenagers, over seeking revenge.
Question: How might the inciting incident, cause our main character to have to make a choice? That is, the invading powers caused our teenagers to be forgotten, AND (riffing here, but maybe) the teenager is the daughter of the main character - then he would have to save her then! Right!