Just to add, if we could reduce the cost of getting materials, fuel, supplies etc into orbit hugely then we could keep it there. Not just a reduction like the one SpaceX hope to do. But a major reduction, e.g. the orbital spaceships of JP Aerospace, down to $310 per ton to get material into orbit. Or indeed like Skylon, that would be enough. If it was as easy to send materials into orbit as to send them to another continent, then we could keep the ISS. For that matter we could even return it to Earth to a museum here, or return modules, repair them, and send them up again.

It’s all a matter of the high cost of sending materials into orbit. And that cost increases as the ISS gets older and needs more repairs done to keep it going.

I think there is a chance that we could get a major reduction in costs to orbit - perhaps late 2020s, or 2030s. There I think Skylon is our best bet, with JP Aerospace an outsider, which I happen to think is in with a chance, but not probably on that timeframe, they are taking a very long view and it could take them decades. And there are other ideas too including use of spinning orbital tethers to reduce costs to orbit.

If we were really confident that it could be saved - we could boost it into a higher orbit, where it could stay up for another decade until we have low cost transport to orbit. The problem is that if we just abandon it, then it gets harder to do a controlled re-entry later on, if that huge reduction in costs to orbit doesn’t materialize. And boosting it to a higher orbit is itself an extra expense.

It was the same for Skylab and for MIR. And in the Apollo program a huge amount of hardware was sent to orbit around Earth or to the Moon, and nearly all (except Snoopy which is in an independent orbit around the Sun - and some rocket stages) either ended up on the Moon or back on Earth. And wherever it is, none of all that equipment in the Apollo program is actually functioning in space, and useful any more except the passive reflectors that the Apollo astronauts left on the Moon.

And it’s not just the ISS, but all the space shuttle launches, and the crewed and unmanned supply missions and so on lots of hardware that is just discarded after each flight. That’s the nature of our space explorations to date. Like having to build a new airplane every time you cross an ocean, and it all gets discarded during the flight, falls apart only leaving the crew’s cabin left by the time it reaches the other side of the ocean. So you’ve gathered together a collection of aircraft cabins on the far side of the ocean, as a result of sending dozens of planes across the ocean - but you decide you can’t maintain them any more because they are getting derelict. Like that.

And everyone involved in building the ISS knew this when they did it.