Re: Station keeping
Mir really suffered from being abandoned - and never fully recovered. The ISS is more modern, but it's not designed to be operated without a crew. And things break regularly - which a crew can fix.
I suspect the answer is that it might be possible to work round some problems - but the longer you leave the station unmanned, the larger the risk that bad things might happen. You've got to keep it at the right altitude, and you've also got to maintain control of orientation of antennae and the solar panels. Once they lost that on Mir, they were always fighting communications and power problems - and I don't know how much better the ISS would be at that.
Plus abandoning ship would destroy loads of long-term experiments.