Don't worry - if these missions are created along the same lines as similar missions, the target POIs will respawn until you've completed your objective.
Besides limpets, another option was to just tickle them until they drop some cargo on their own.
Technically, yes. Practically, no.
Technically when you damage the hatch, there is a chance that a random cargo cannister falls out. That chance gets higher the more damaged the hatch is.
Practically, you're going to destroy the ship by collateral and bleed damage before the right thing falls out in 9 out of 10 cases