Having done the Dempster Highway in the summer of '18, I can now report that in the summer the highway is a mud bog when it rains and until it dries, but it dries fairly quickly. Mud guards in my opinion are senseless to use. I took mine off actually on the road! The guy I was travelling with did not have mudguards and his bike did not clog up like mine did. I was stopping every 20-30 minutes and spending 10 minutes trying to clear my rim brakes, and free up my derailleurs. Disc brakes would be a better option for this ride, but rims brakes were fine. I did have to replace my pads twice because the mud is very abrasive and shredded the pads from all the mud buildup. It was a tough slog in the rain, but a joy when the sun was a out. The Dempster ends at Inuvik. The new section of highway that continues to Tuktoyuktuk is the same road surface as the Dempster. That section is called the ITH, or Inuvik Tuktoyuktuk Highway.
It is well worth doing the ride all the way to Tuk and the Arctic Ocean if you are a serious cycle tourist. The scenery is some of the best you'll every see. It's tranquil, great wild life, yeah mosquitos but use an original bug jacket and you'll be way better prepared than most others.