Well we could still go and drive to the winter gate: http://goo.gl/maps/3xEub
A perk to doing that is there will be just about zero traffic.
Another option is the BMW CCA is having their mountain twisties tour that same day, meeting in Issaquah. I'm just concerned that drive will be a little too calm for my tastes.
I'll probably just stick with our plan but we'll have to see what the WSDOT can do. They have 25 days to get this sorted out so hopefully that's enough time.