Swooping Hawks Grenade Pack Question

So in the grenade pack entry it says that the grenades are a separate weapon that do not exclude the character from firing another weapon, which is fine and good. After that it says that you must fire at the unit that had the grenades dropped on them if possible.
What if:
1) Unit is destroyed by the grenades or something else before you shoot the hawks?
2) The hawks are dropped in a way where they do not have line of sight to whom the grenades were dropped?

Does this allow the swooping hawks to fire at a different target in either of these cases or am I reading if possible too liberally?

I think so yes.

I would assume you are free to hit anything if that target is already gone. If you were unable to shoot any other target, it should be written as "the unit may not fire at any other unit in the shooting phase" ... or whatever the wording in the BRB for shooting then charging is.