I get the frustration. I really do. I had an older Maxima some years back and the floor panels are/were soft, and hot to the point I had to replace them. It never made it to a recall, but a very prevalent TSB was issued to Nissan Techs or any tech using software that picks up or allows access to TSBs.
Cars rust. If rust isn't tended to early enough on, it literally turns into what you're dealing with. Premature rot and rust can be considered catastrophic [just ask Toyota who had to buy back millions and/or replace frames]. With that said there really aren't any recalls for the Nissan rust issue, mainly---because, in your case, it was neglected, for what I would say, would be years. I am in total agreement with others that already mentioned the service tech you deal with, absolutley dropped the ball if you truly didn't know anything about it.
I used to be service tech in my younger days, Bd it's a case of CYA when something rolls in the shop with next level corrosion, especially in subframes, brake lines, gas tanks, floor pans etc.
To me, in my own experience, this car should have NOT passed state safety inspections the last 5 or 6 years or at least early on in that time frame I'm using, and tech shouldve notified owner notification of excessive rust/corrosion---in writing if they were willing to put a sticker on it. Normal routine maintenance, other than inspection, should have picked up on this as well [oil changes, brakes, tires] and had this in writing also if noticed, as again most places instill CYA in all their technicians.
Nissan America will give you a case number with any driveability/safety issue, as they are required by law to do just that. You can also report it on the NTSA website, but nothing will happen---unless there IS a recall.
I didn't read every line of every post, but was this a used or new purchase [i.e original owner] as I've seen vehicles roll through the shop, used purchases, that were pushed into auction lots after flood area claims. Does it have a salvage tag on it?
Any who...you're right about one thing, if you were on the highway when that let go, you wouldn't be posting about it, so you're lucky. Think it's time for reassessment, think logically, go through your maintenance records and see if anyone ever took note of the front end/undercarriage. Then maybe speak with someone at the state DMV/safety officer who can file a report against the shop, and sometimes---if this was blatantly missed, suspend the safety inspector. If it's gets there, than you may have something to go on, if negligence is found from the state safety officer, who can then advise you.