Obviously the best way to keep these machines preserved is to be able to fly them, have them do what they were built for. But that’d be in an ideal world, which we are far from. Also some, such as the prototype mossie for example, are perhaps too historically significant to ever consider flying.
If it’s a historic aircraft, living in a museum, then it’s worthy of whatever preservation, restoration and general maintenance it requires. Be it a flyer, taxiable, static, cockpit section, or even a wreck sat in store waiting for it’s turn, to me it’s an artefact. And the museum has a duty of care towards it.