I'd suggest letting your dad's insurance pay for the repair.... if you want to take some of the 'sting' out of it, pay his deductible. all depends on who's insurance is better able to deal with it.
As someone else said, you really need to find out what sort of effect a crash would have on your rates, before you decide to avoid ins altogether. If it doesn't change your rates, it's the whole reason you have insurance in the first place, right? All of the riding gear needs replacing, too..... that's easily another $600-1000, right? (retail?)
As you were not riding it, how can you be at fault?
If your dad needs to go to PT, or surgery (knocks on wood) the financial consequences can mushroom quite nastily. Far better to have a claim in place, methinks.
Worst case, your rates go up. Even if they doubled, you'd be better off once you go 'big picture' on all the associated costs. As I said, I don't believe your personal rates would be affected, as you were not the operator. Dad is a licensed operator and simply lost the fight with gravity. You are not at fault for that.
At least make the call, and explore the idea. "Hypothetically speaking......"