During the three times I driven the Cassiar Hwy. I never encountered any mud pit where they are doing construction even while it rained hard thru those areas but I am stating short of not potentially encountering a situation like that cuz sometimes you never know.
The northern half does not have any lane markers or center line and can get a little bumpy like frost heave surfaces which I drive pretty slow along these stretches, and the southern half of the highway has lane markers and is usually smooth surfacing roadway......as noted the entire highway has no wide shoulder at all.
Travelling in the far north can be a crapshoot as far as encountering any of the elements related to road surfaces, construction zones and weather as the Cassiar is no different, I would just check up on the Drive BC website for the latest info once you get there and ask the travelers upon arrival at the Junction 37 station (they are open most of the time as every once in a while they do close with no warning).
I plan on travelling on the Cassiar hopefully next month if I can get approved time off work rather than September in which it is like pulling teeth to get granted time off even then with my line of work.
The only thing that will stop me from travelling the Cassiar Hwy. by the time I do is if there is actually some form of road closure, in most cases you should be fine.
Just don't go off the Cassiar Hwy. like this buried backhoe did just south of the Stinkine River (at the top of the grade) or otherwise you will end up in a dry mudpit like this rig and be completely stuck :
1975 Ford F250 2WD Ranger XLT (Owned June 2013)
460 V8- C6 Trans- 3.73:1 (196K Total Mi)
2000 Fleetwood Angler 8ft Cabover
Air Lift 1000 (Front)
Hellwig 3500 lb Helper Springs (rear)
Hellwig Front and Rear Sway Bars
Goodyear G971 LT Series (siped)