If your pH drifts that much in a week, sure. With 50ppm borates, my pH moves very slowly.
Water chemistry should be the least of your worries.
If there is any possibility of freezing temps, unless someone is going to check your spa every day for you to make sure it's still running, it would be foolish to leave it filled. GFI's can trip for a multitude of reasons and if your tub shuts down while you're gone and no one is there to reset it you are leaving yourself open to freeze damage.
In fact, here in NY, I tell my customers who want to use the spa year round that during the colder months they must check it everyday to see if it's still running. After 21 years I can't begin to tell you how many times I get a call from someone in Feb. saying they hadn't used the spa for 2 weeks and now it's frozen solid. Or a call in April saying they thought the tub was running all winter but now it's empty. Freeze damage because no one was watching, the GFI tripped or something else went wrong and the spa froze.
Your spa, your money, your call, but unless you have someone to monitor it, winterize it.
I would keep it running i am in Spokane, we get colder than you guys on the coast , there would be no question , when i go on vacation in December i leave my D1 running , never had a problem, even when we lost power last year for a week still no issue, good advice to put some chlorine in there, have a great vacation