> If models had persistent memory or an evolving set of weights, you could easily construct an argument that they can experience "suffering" or other emotions which resultingly adjusts their personality.

They do, during training

Is the ability to form and retain long-term memories a necessary precondition for rights in humans though?

Incinerating demented people is highly ethically questionable (even if you could be sure that the subjects have no memories left and are unable to form new ones).

So if a human loses their memory and their neutral plasticity (with age for example), then they are no longer capable of experiencing suffering?

A model detached from a harness, sure. But we routinely do add persistent memory to systems incorporating LLMs.