Re: ISS' swansong?
Assuming that the ISS will truly be deorbited a few years from now, it seems rather obvious at this point that this would mean having only a Chinese space station in LEO by the end of this decade.
To be fair, this depends on your definition of space station.
Each SpaceX StarShip will have approximately the same internal volume as the ISS does now. Albeit they don't (as standard) have anything like the number of docking ports, remote manipulators (Canadarm/Dexter) or other science-oriented facilities.
Compared with the hundred-billion dollar process of building and launching ISS in pieces, if NASA want a new LEO space station, the easy route will be to simply ask SpaceX to fit out one or more Starships for science operations and long-term habitation (which they will be doing anyway for Mars Transit), launch to LEO and dock them together. Indeed, you could launch a dedicated docking bus on a freight-Starship which arbitrary habitation variants could dock to.
Depending on cost, it might even be practicable for a crew to fly up in their own Starship, dock and have access to other vessels and "station power" and then go home in their Ship (rather than doing crew changes via small capsules as present), bringing back science experiments whole and allowing periodic updates/overhauls of hardware and living quarters on the ground rather than having astronauts do it on-orbit.
A strategy of assembling ships into a station would likely be the basis for a Mars space station should such a thing be found necessary. Starship is sufficiently massive that in the near future the architecture may flip so that "space stations" only consist of a dedicated docking hub/port facility (possibly with power and other amenities) with the majority of volume accounted for by the (semi-permanently) docked ships rather than small crew capsules docking to larger permanent stations.