If you are good rider it's safe to ride a bike but drive it safely because road is smoky in some part and too much of curve way..it will be abit problem for campsite and fooding..i would better like to suggest you to stay somewhere in Shillong and then just go for sightseeing in dawki.
Your ideal itinerary should be like:
Day 1: Start from Ghy and stay put at Shillong. Visit Elephant Falls etc.
Day 2: Start Early. Ride to Dawki. Enjoy the beauty of Root bridge and the cleanliness of Mawlynnong, Asia's cleanest village enroute. Start for Shillong same evening.
Day 3: Start back for Guwahati