How do you know when a unit is wiped out

Hello! So I was watching Legend and he'd occasionally go "ok that unit's wiped out, that's not coming back after this battle" when he's not referring to something that's Shattered, as in something that's lost enough models to no longer function after the battle ends.

Is there some icon or something to know this? Or does Legend just have enough knowledge to kinda guess when somethines been fully destroyed.

Thanks for reading