I'm pretty sure Rio tapped out on Argyle as they had worked their way through the entirety of the alluvial deposit after 35+ years of extraction.
They were very keen to find a lode source kimberlite pipe and get more pink diamonds but sadly .. no show (as of the last time I looked at the Tech. Reports on regional exploration).
There was absolutely a financial element on the decision to shutter and rehab the mine site .. but it was driven more by diminishing returns at that deposit than by market starving.
They don't seem to have any plans to reopen as they're supposedly going into full rehab mode (all equipment gone, return to nature):
https://www.riotinto.com/en/operations/australia/argyle