Paper spacecraft can do anything. Buran was designed for the same mission lengths as the Shuttle, on the order of a few weeks at most, not half a year or more. For long mission durations, storable hypergolics are the way to go for now. We don't have good flight time on anything else, and we need that for something we're putting crew on.
> For long mission durations, storable hypergolics are the way to go for now.
Soyuz is a counterexample which flies for decades. Lockheed's engineers working on orbital fuel storage (Advanced Cryogenic Evolved Stage) will also point that it's not a law of physics.
