Armin's probably going to die. This is what's gonna happen, I think
After a long winded battle with the titans, mikasa, eren and armin are cornered.
Armin comes up with a genius plan and tells mikasa and eren about it, he knows that he's going to die from it, but doesn't tell the other two.
He knows the only way that mikasa and eren can get out is if he triggers eren's titan power to get out.
He dies in front of eren, smiles in eren's eyes before being swallowed by the titan, and eren becomes enraged seeing his best friend die.
Mikasa and eren escape, fueled by the power that armin's death gave them.
They look in the horizon at the end of the chapter and vow they will reach the basement to avenge armin.