Well, Robert/sevoblast just posted a restoration project he’s started for a 40 year old Sherman, commenting how it has stayed similar all these years. From the recent few examples of Sherman builds I’ve not seen any indication that the molds are failing.
Tamiya has gotten really good mileage from those mold masters and I don’t see why they wouldn’t throw it onto the injection molding machine every now and then to make another batch, as each of them is already a sunk-in investment.
There’s a recent announcement that Heng Long would be shifting towards making tank models in turn rather than making everything at the same time, but I suspect Tamiya has already been doing so.