For the easiest solution (besides a tub-sitter), I would advise draining. It'll be a lot nicer to fill with fresh water, than to potentially troubleshoot a gunky spa.
Blowing pipes out would probably be helpful (I don't know if it'll be worth the effort).
I recommend leaving the cover in place to keep debris, etc out of your spa.
I am NOT one of the true chem experts here, one of them may have better advice.