Could the space shuttles have been left in space and used as temporarily visited space stations? One could put a modified spacehab in the cargo bay, with solar panels and with which the Soyuz/Dragon could dock. Wouldn't it have been a cheap and capable alternative to the ISS? Could its systems for life support et cetera work long term? Could they have been put to better use than as museum pieces, with some planning and minor modifications, or is it completely crazy? (I realize that they are not launchable anymore).
Or maybe more realistically, couldn't they simply have been left as modules docked to the ISS? They would've provided some extra working space for the crew, boosting capability for orbital station keeping, RTG power, cargo handling, independent life support and an emergency landing system. The whole point with landing them was to reuse them. Well, they weren't reused after the last landing, so they should never have been landed the last time.
Endeavours last visit at the ISS, seen from Soyuz. Could it have stayed there?