I've spent quite a lot of time over the past few days and, in summary, exporting all stems using the channel option seems the best way of "archiving" the tracks so that if a plugin or instrument fails in the future you'll still be able to re-mix or remaster the track. So, in effect, what
@FMN-Music has in his video although just doing that step is good enough for me.
The other option that I would have liked to explore more is to do a "mixdown selection" on each and every track because if you then played all the resulting tracks without any routing you would get exactly your mix (minus any of the Main Out plugins). I'm not exactly sure where that would be useful but it would be nice to have that option. Unfortunately, though, I couldn't find a way to make a macro which would automatically do this to every track in a song. Maybe there is but I couldn't get anything to work.
And, before anybody suggests it, exporting stems with the track option doesn't achieve it.
As a total aside, no rendering option nulled, especially in the 1k+ frequency range which is making me wonder whether I need to test the rendering processing although maybe that's just to be expected.