Haven't been on the Cassiar this year, but from past experience can state the washouts are usually well-repaired by crews.
On two occasions we were in groups of vehicles escorted through washouts on the Cassiar Highway while the water was still running across the highway ... ground was firm though and we all made it fine. Excavator standing by to continue with repairs.
This recent incident seemed to be high water just sitting across the highway, rather than streams running across the highway. Likely no problems driving through there now that the water has receded.
On the Alaska Highway between Whitehorse and the northward turn-off to the Klondike Highway the water did the same a couple of weeks ago. It has receded and the highway is fine.
Even the portion of the Alaska Highway near Mendenhall west of Whitehorse that was flooded a few weeks ago and closed is open again and also fine to drive across.
Water is high in many places ... for those heading to Alaska, check the weather alerts for the central and east area of the state ... high water is threatening as it often does this time of year.