I'm no expert, but last I heard from a buddy at the C&TS a lot of work is needed on the Flanger gear, particularly where it mounts to the frame. Along with all the gauges and external appliances needing to be re installed on the Rotary, due to them being removed a few years ago because Someone tried to make off with the backhead gauges in the middle of the night, IIRC.
I believe a Hydro would also be in order, along with most likely a entire winter worth of restoration work, not to mention a great deal of wood replacement in the shell i would assume after it has been rotting outside for twenty years, despite the efforts by the Railroad and the Friends to keep it from doing so.
IIRC she also needs a new injector on one side, that injector now on the 463; so a new one would have to be sourced. As I heard it awhile ago, there was a plan to refit OY with a cross compound air pump instead of her single pump to make the Rotary a closed system, instead of having to rely on pusher locomotives to make up the difference of air pressure. I think work was started on this conversion..? But it was never finished.
I'm sure John West could give you a much more detailed report; but TL;DR: I don't think it is in "Plug & Play" condition, though it could be much, Much worse.