I am thinking about a trip to North Peak. Many years ago I remember a road around the west shore of Saddlebag lake is this still there and is it feasable (legal) to mountain bike to the back of the lake to get a jump start to the base?

Check out the page here on SP. There is a road to saddlebag lake. From there you can hike or take a boat across. But boats start working after 7am if I remember correctly (most likely not, since I never took a boat myself). It is a beautiful peak with short access, enjoy.

As it relates to riding a mountain bike across that...I'm trying to remember what the approach trail next to the lake was like the last time I was up there (2009), but regardless, the most important determining factor as to the ability to MTB it is whether it is in a wilderness area or not. Check a map on that and you will likely have your answer

The west shore is solid rock and wouldn't be much riding there. The east shore is the old road, the wilderness boundary is at the back of the lake by the old cabin. I've seen people ride bikes in there before, but it would be almost as quick to walk.