To LLMs specifically as they're now? Sure.

To LLMs in general, or generative AI in general? Eventually, in some distant future, yes.

Sure, progress can't ride the exponent forever - observable universe is finite, as far as we can tell right now, we're fundamentally limited by the size of our light cone. And while in any field narrow enough, progress too follows an S-curve, new discoveries spin off new avenues with their own S-curves. If you zoom out a little those S-curves neatly add up to an exponential function.

So no, for the time being, I don't expect LLMs or generative AIs to slow down - there's plenty of tangential improvements that people are barely beginning to explore. There's more than enough to sustain exponential advancement for some time.