On two NPCs out there: one NPC already increases your firepower a lot. The increase of firepower with two players using the SLFs is justified. Those players could just as well mean you have two more full sized ships in your wing, which is more firepower and durability thatn the SLFs. But with NPCs, consider that each of those ships in wing can also then deploy not just one but two SLFs.
It would be just one more step on the endless and worthless ladder of power creep. We don't need that. The other part of the suggestion: anything to save NPCs at ship destruction would be welcome. I mean, you engineer your ship to the limit. It's an absolutely one-of-a-kind ship, with only a few extreme experts throughout the galaxy being able to make these adjustments. But you can just rebuy it. But the crew member next to you never enter the escape capsule when you eject?
But i am not sure if engineering is the answer. The cheap and easy way for FD would be to add the NPC to the rebuy. Let it cost a million or two, it's oki. Or if you want more, create gameplay out of it. Mark the NPC as "missing" in the crew menu after ship destruction. Then you get a mission chain to recover your crew. This can be just one one mission, e.g. go to station XY and pay the rescue service. But it can also result in a longer chain, e.g. criminal syndicate YZ has your crew, they want you to go to system A, take down rival criminal leader B, recover item C and also, as you are out there already, bring along rare good D from system E 150 LY away. And this might even branch off, so organsiation Q can give you a hint where they hide your crew, so you can instead go there, interdict that ship, use a hatch breaker and rescue your crew directly.
When you completed your crew rescue, the "missing" is removed from the crew menu and you can put them to active duty again. (If you don't want to trouble yourself with the rescue, you terminate the contract and hire new crew. Bad commander...

)
The options are manyfold and even the game mechanics for this would already exist. I really wish that something like this would be implemented.