I see an argument for any one of those.
For either of a or b, you could say we got through 2016 without, and you're likely to draft a fairly solid prospect on defense, if not a couple, seemingly automatically making the team better.
And of course, the same "we got through 2016 without" logic applies to C, plus you're likely to be able to replace him through FA with the savings from cutting or trading him.
For d, it's less empirical, more assumption, but the argument could be put forward that the player personnel side now has sufficient assets within it to withstand losing one key piece, and that Jerry himself has evolved to listen better to his advisors, not the least of which is the presumed future owner, Stephen.
Then again, how good could this defense be with either Smith or Gregory? How much better could it be with both Smith and Gregory?
Then again, what an incredible advantage it is to go into a season with not 1 but 2 bona fide Pro Bowl caliber QBs on the roster? Moreover, given the multiple lessons of rookie QBs that have come back to earth in very recent history, at least to some degree and notably for some, to a large degree.... why wouldn't you value that advantage pretty highly?
And, then again, why mess with a key piece of the player personnel machinery. If it's only about 2017, maybe so, but it's not. We want to win in 2018 and 2019 and on and on, and what-if McClay would prove to be too much a key to that machinery... that, without him at the hub of the engine, it all falls apart? Do you really want to risk that if you didn't have to?
Having said all of that, for me, it comes down to the fact that it's too hard to find an excellent QB... too hard to find an excellent pseudo-GM/player personnel guy. I decide between Gregory and Smith... which one do I think has a more substantial ceiling. I'm probably more inclined toward Gregory at the moment just because I've seen him on the field, and it's clear to my eye how Haley-like he is... and DE is the conventionally-understood position of need for us. That seriously frees me up, then, to draft BPA this spring.
So, I'll go with "a"... I would take b, c and d instead.