Setting total realism aside, the core of the idea is to create a high pressure extraction. If insertion/extraction are linked you would know that you are likly to encounter hostiles on the approach while youre flying a vunrable heli such as the Blackhawk/Hind forcing you to make good use of your AI wingman Apache/Havoc.
Yup - but the second way you get the same "insertion threat" for both extraction and reinforcement missions in addition to providing, as arneh mentions, the same kind of possible threat to the insertion side (are we heading to a key site trying to escape or a key site digging in). I think we're all agreeing, just using different words (and adding different levels of mission)

Search and rescue may give you the same thrill, it that was added. Then you could also have a time limit before the crew was captured (depending on how far they are from enemy units perhaps). And could be made fairly realistic.
Maybe even would be cool if the crew to be rescued set off a smoke grenade or fire a flare as you came to pick them up, so that you can see where they are

Dropping in on the red smoke - sounds like a blast

(night-time rescues would naturally need a strobe instead!)
Perhaps it would also be possible to have a reaction created (as it is for other mission types). Once an enemy unit is shot down, dependant on varying survivable conditions (package height, possibly terrain, type of damage) the attacking side could create a response ground movement to the area of the "downed" unit - adding not just a time limit, but an imminent threat to incoming rescue units (especially if the nearby forces arneh mentions are mechanised or manpad based and move into the rescue area).