I think there is a good chance that it will be updated. But you can´t be certain ofc. My advice is to inspect the new monitor sent and after setting it up, then look for faults. Asus support have been very helpful with me and told me that they will swap again, if the replacement monitor suffers issues. I would not worry to much and instead look at what happens.
I was never aware of this issue, mainly becuase I bought mine in 2018 (I reckon mine had been updated?) so again I reckon those refurbished ones that had issues, would get the update and then the one taken in, would get the same threatment if needed.
That is just my take ofc.. Take pictures when you take the monitor out of the box and as the first thing, go look for external damage, then go look for Backlight bleed, dead pixels, etc
Again Asus have been very supportive towards me, as of now I have only had good experience, albeit no monitor swap yet, but I know the drill from their instructions.
I hope your issue gets sorted out
Edit.
I found this
https://rog.asus.com/forum/showthread.php?104402-Asus-pg279q-FirmwareI reckon you should not be worried about not having the firmware update. Mainly because I don´t think that 4 year old monitors, to make an example, would not be fixed with the update, as that would most likely be one of the reasons for RMA
