This question really needs to stop lol. "Declining numbers" is a valid concern for some series. OP is not one of those series. Nevermind the fact that OP is still an incredible seller, it has contributed so much to the magazine, being its face for over 2 decades, that even if it somehow dropped so much that it became one of the worst seller in the magazine (which is an impossible scenario unless it keeps going for like 15 more years), it still would NOT matter and it would be allowed to continue as much as Oda deems it proper.
It's a kochikame case. Sometimes a series is just so important that sales just do not matter. Kochikame was hardly a big seller by the time its ending came around, yet not only did the axe never come, its ending was treated as an unprecedented event within the magazine. And I'm sure when OP does end they'll probably find a way to one-up that treatment.
Seriously, let's just move on from this. Enough words have been wasted on this. OP is not getting axed, ever, end of discussion.
As an aside, this is a pretty good hold for OP like I said earlier, this volume should fall somewhere between 95 and 94, decent recovery. And as expected, KnY 1 crossed 4mln, series is an absolute monster.