I think this article is slightly misleading-

Aardman doesn’t use any run-of-the-mill clay when crafting their feature-length films. Newplast is a nylon-reinforced clay that doesn’t require the same steps other similar materials need, like glazing and firing.

It sounds like they are in trouble if they want to continue things the way they've been doing them, but they can look at other options. So it's a problem, but not necessarily one that will end Aardman. They could always do things like adopt Will Vinton's Claymation techniques. Or go the Henry Selick route and have a lot of solid interchangeable parts for his characters.

So I think we shouldn't be so pessimistic and think Aardman will only ever make one more movie. I am sure they are already exploring other avenues.