I've received an email today saying:
Originally Posted by Hilton
AN UPDATE ON YOUR HILTON HONORS STATUS
Hi Ldnn1,
I've got great news! Your Diamond status match with Hilton Honors has been extended through March 31 2019. It's our way of saying thank you for staying with us...
bla bla...
I have only completed 7 stays under the match so far. I have my 8th booked for this weekend but will cancel it if not needed.
Do you think it's safe to rely on the above and cancel?
I'm not sure if they have genuinely waived my 8th stay requirement, or if the email is simply pre-empting my upcoming reservation. However the email is very clear that my status has been extended already and there are no caveats in there about completing future stays.