I had ALL Voyager card when I was in living Europe and booked for stays beyond the membership date, with similar warnings (I hadn't realised or worried too much - can't remember which). I didn't want to renew as when I bought the Voyager card I didn't know it didn't stack. Long story. Anyway, didn't renew and when I stayed - I think at 4 or 5 bookings, no one ever asked me anything about it. I had by then though re-purchased my Accor Plus, so maybe because I had a PLUS membership (rather than the All + membership) no-one noticed. I am really not sure. But zero eyelids were batted, so I had a _feeling_ that it was more talk than anything.

Your situation is a little different because I did book with Voyager rates - which look like normal accor discounts, you see the -20% Accor Voyager rate banner. The issue for you might be if you book RHR because those are definitely linked to Accor Plus. And then on check-in, on then the other thing to consider is that on day you check-in, you get the perks of whatever you membership is at that time. So you wouldn't get any Accor Plus perks if you don't renew, but you would get your status perks. There are very clear codes on your check-in docs so that the staff know your exact status and memberships on the day of check-in.