Yep. The
lahar that would occur if the western face of Rainier let go would take out many small towns and go all the way to Puget Sound, possibly even taking out the Puyallup River Bridge. That'd completely cut off north-south access on I-5 for Seattle. Depending on how wide that collapse was, it could even possibly take out more towns along the Nisqually and possibly destroy the I-5 bridge over that river as well.
Scary thought all the way around