I made a quick run through marine action cards - i bet one of them is "Suppresive Fire" - Target any Tile within LoS of any Marine Model. Any Model moving onto the Tile it is instantly deactivated. Yes, your point of view is totally legit, this card is in action until at least one marine model has LoS to the targeted Tile. Its a very good tactical, and movie-like action - marines making the last stand ect. i like it
The second card i think is "Covering Fire" the similar thing but you got a chance of autohit the enemy instead of deactivating him. The same thing as above - any logic would point that it is valid until any marine model has LoS to the tile - Those two cards are really usefull
