The nice thing about the
road to the Marion Mountain Trailhead is that it's paved the whole way. You do have to park off the pavement though. If anything outside of Idyllwild proper is open, it will be the Marion Mountain Trailhead road. Of course, you have to get a wilderness permit, so when you contact the ranger station for a permit, ask if the road is open.
If the road to Marion Mountain is for some reason not open, you could just take the Deer Springs Trail. The
Deer Springs Trail starts right on Hwy 243. There's no way that's going to be closed.
HJ