This basically. Either there's a functional commercial replacement which is theoretically also a use case for a properly functioning Starliner or the ISS gets extended. Plausibly both. It doesn't have a fixed life limit, hasn't stopped working, hasn't stopped being used for experiments, and a commercial space boom era when microgravity experiments started turning into businesses would be a weird time for the US to decide it was a waste of money and give the space station monopoly to China...
The ISS may not, but Starliner does have a fixed life. It is meant to fly on the Atlas V, which is end-of-life. Once those are gone Starliner would need to be integrated and recertified to fly on a new rocket, probably Vulcan, but it's doubtful Boeing would want to spend the money to do this.
In response to your other point, I am very skeptical of microgravity experiments becoming a big industry. I think NASA (as an organization, I'm not talking about individuals in NASA) is mostly interested in continuing human space flight simply because it keeps the public interested in space, which makes NASA's funding more secure.
