I have heard about Abena dropping M/L4s so many times by now that I don't give it too much credit anymore.
Firstly, as much as I enjoy how M4s fit on me, their quality has gone downhill a lot compared to a few years ago, and nowadays there are plenty equally as valid or better alternatives on the market, so even if they were to actually be discontinued it wouldn't feel as a tragedy to me.
Secondly, the owner of the place I usually get them from (Save Express) when I personally visited them last July told me they'd have been out of stock since mid-September and guess what, when I was back at their warehouse in late September M4s were still there, and they are still available today on their website with no apparent restriction on the amount you can buy.
What I've been told about the quality getting inconsistent is that, while in the past M4s used to have their own production line, now they share the machinery with other products, so the machines have to be readjusted every time they switch production, resulting in an imperfect calibration. I've also been told that Abena has been considering outsourcing them, as they already do with AbriLet boosters, which are now rebranded Lille boosters, half or 1/3rd of the thickness and absorbency of the old, real, AbriLet Maxis.
So... I don't know. In the past I used to stock up big time on M4s because I really liked them and they were the diaper I'd wear 90% of the time, nowadays I stick to buying a few cases at a time knowing that there'll be some disappointment compared to the quality of the previous batch, and keep some variety at hand. Betterdrys, Rearz, Molicare, ID Slips, there are so many valid alternatives out there without the issues that M4s started developing.