By “last call” does that mean last call for orders, or when Nikon shuts down production? (Assuming they haven’t already done that.) I am a little surprised that complete DSLR production is winding down so quickly. I figured that certain niche products like the D6 would be in production (or at least in stock), along with a small selection of specialized lenses, for a few more years.
I am old enough (bought my first SLR in 1972) to realize that technology changes in photography happen very quickly. Back around 1990, a lot of people initially dismissed those plastic AF cameras and lenses as "junk," but the world transitioned to AF very rapidly and Canon quickly took over the #1 spot within a year or two due to their superior AF.
In the few years around 2004, sub-$1000 DSLRs quickly took over as the quality from digital became "good enough." Film SLRs were mostly abandoned within a couple of years and turned into a niche product, but at least the lens mount didn't change in that occasion. Nikon introduced their very last film SLR, the F6, in late 2004.
Canon and Nikon introduced their FX mirrorless systems in late 2018, within a couple of weeks from each other. By early 2020, both brands introduced their very last DSLRs, namely the 1Dx Mark iii and D6 for the scheduled 2020 Tokyo Olympics, but Covid interrupted the Olympics as well as the camera market. By the time we recovered from Covid about 2 years later, DSLRs were mostly history.
I am not sure what the next disruption will be, perhaps video or perhaps something (AI??) I can't even imagine now, but any transition will be quick.
If Nikon is completely discontinuing F-mount products I sure wish they would get a true Z-mount equivalent to the D7k cameras, and even the D500. (The Z30/fc/50 models don’t count, IMO.) At least one member of this forum moved on to another brand to get better-performance APS-C gear. For various reasons I prefer the DX to the FX format. I will be sticking with my D500 and DX and FX F-mount lenses for the time being. Given that I still have and sometimes use Nikon 1 mirrorless gear, Nikon has to give me a compelling reason to move on to a third Nikon digital camera system.
If you are happy with the D500, stick with it. I still have one but haven't used it for a while. I can no longer tolerate 10fps (too slow) and all the noise and vibration from mirror slap. Nikon has made it very clear that their emphasis is on higher-end FX mirrorless. I have no idea whether Nikon will introduce something DX that is considerable superior to the Z50, but IMO it is unwise to count on that. For those who prefer APS-C mirrorless, Fuji should be the brand of choice, provided that you like retro. Otherwise, Canon and Sony will likely provide more APS-C support than Nikon.