Will the res agent know about this drill?
Absolutely. And since you now know it too, this is all straightforward.
Will I automatically get assigned a C ticket, or would I still have to do all the checking myself?
Will still need to do all the checking, as NWA does not permit waitlisting.
Will it work if I buy a perkpass (100K) anytime coach ticket?
Not at all. You need to get the 100K WBC award - anything else would require a cancel and redeposit of the entire award booking, with a possible permanent loss of any seats already confirmed in Business Class.
If I don't luck out, do I get my 50K back?
If no seats have opened up, say, 3 days or so before the flight, speak *directly* with a NW supervisor who can either get Inventory Management to open up seats or, failing that, adjust your award to a PerkSaver Coach award level. But this all needs to be done before you travel, of course.