Oh, so you
can tell I've watched too much Mythbusters?
That's going to be some photo -- just the Roadster orbiting around Mars/Sun/Earth.
If they do leave it unprotected, I.e. planning on it degrading quickly. I don't know which path they'll choose.
You know, one thing that I find kind of interesting.... so what happens when the epoxy binder in the CF degrades? There's almost no torque on the thing. Some trivial tidal forces as it passes by planets, but that's about it no? Would the CF fabric even come apart without its binder in space? I guess if there are some internal stresses.... I guess you'd also get some thermal stresses as the vehicle rotates, one side going into sun and the other shadow at periodic intervals. And minor centripetal force, too.
The glass shouldn't degrade. But thermal stresses will be high if the car is unprotected - it might not even need minor impact damage to weaken it enough to crack. Now, it's lamintated glass... but laminations are plastic (not even vacuum rated); eventually that'll degrade enough in the high UV flux that the glass debris cloud slowly floats away.
(Thinking about thermal stresses - maybe it might be smart to spin the vehicle up. Keep it rotating fast enough that no side is left in the sun for very long, so the temperatures average out. It'll also then keep a fixed orientation rather than tumbling.)
The debris aspect may sound bad, but we're talking a ***very*** large, very empty orbit (MTO). It'll take an unthinkably long amount of time for the debris to distribute its true anomaly (position in orbit), and even then it'd only be spread out along a single orbit in a ***very*** big range of potential transfer orbits.
I find it kind of funny to think about the tires (assuming they leave them on, deflated). Any small amount of air inside, or outgassing air, will reinflate them (assuming the valve stems are on) - to an extremely low pressure, but they should recover their usual shape, in theory at least. Of course, they're not rated for vacuum exposure, or the high UV/radiation flux of space. Like plastics, they probably won't last all that long.
I really hope NASA takes the opportunity to try to photograph the Roadster upon closest approach (for example, with MRO). I assume HiRISE can target objects in space? It'd be great for those "astronomy image of the day" pictures that are used to raise public interest.
Oh, one more thing: would be nice if Musk installed a couple corner-cube reflectors on the Roadster. Then you could do laser ranging to it, which might some day be useful for e.x. gravity or solar wind pressure studies.