I had this same problem.
After doing mission many times I noticed that when you blow up the last tank,if any crew member bails out before tank goes boom,then trigger fails to kick in.
I've tried repeating this a few times to make sure and it seems that every time the mission fails to end is because of this.
Going down and shooting the bailed out crew after the tank blows has no effect either.
So if you see a crewman pop out after you call strike on tank you can be pretty sure the end won't trigger.Just go back to the last auto save and try again.
My tip : I aim the laser just to the front of tank as it comes down the road facing me.When the strike comes in it hits front and top turret toasting the crew nicely
Hope this helps someone.
