Is it me or most mission are going to have 2 primary objective pretty much by default?
I mean you need to do whatever it is you need to do... but than you also need to reach an extraction point of some sort or get out of the danger zone or whatever.
And in fact, it might be harder to reach the extraction point once you've killed the enemy general/kidnapped the dignitary/stole the pricless relic then it was to do the task in the first place, has odd are the enemy is now fully alert and looking for you.