Well, yes, hopefully the sandan disarms you (although even they have bad days), probably more likely to occur when your fellow kyu student fails to disarm you (has happened to me more than once)---I guess you could instead just let go as well and hope it doesn't hit you or him in the head, but I prefer to hang onto it.
I was uke during part of a shodan test this past year, the part where nage takes uke's bokken during a variety of attacks (uke's choice) and nage's choice of technique. I didn't think much about it, since I'm comfortable doing rolls or breakfalls with a bokken, until I realized mid-technique he'd chosen koshinage at one point. Koshinage is my favorite technique to take ukemi in, but I'd never done it with a bokken before; I avoided wacking either of us, and it was fun once I realized I could do it
. He later said he hadn't thought about it either, it just happened. Guess it is important not to think too much.