According to the BBC they can’t actually “take away” the HRH bit, but the agreement is he will no longer use it - which is the same with Harry. I wonder if there’s still scope for others to refer to it anyway?
https://www.bbc.co.uk/news/explainers-59993936
There’s no good outcome for him, and I assume he’s now guaranteed that his daughters won’t get to keep the ‘royal’ treatment he wanted for them if/when Charles’s slimline monarchy comes to pass.