If your entire squad is eliminated, it seems you don't necessarily have to stay all the way to the end to get a reward.

I have quit mid-way after my squad is eliminated and still got a salvage item as reward.

That being said, i think the chances to get a reward after quitting mid -way is tied to number of objectives done and survival time. When I quit early, no rewards. But when i quit later in the match i tend to get a reward (even if not extracted).

Note that for the "complete 3 matches" challenge, you have to stay on until extraction (if your team is eliminated, you still have to stay to spectate), otherwise the match will not be registered as complete for that particular challenge.