As I recall: if Mount Rainier (14,400 feet) were to blow, the entire mountain would simply be gone (just a hole in the ground) - not like St Helens which only blew off part of the top. Seattle and Tacoma would just ‘disappear’ under the debris and mud flows.
Few would listen, as they would need to evacuate Tacoma, Olympia, Seattle, and many other small cities and towns.
As of some years ago, they were only semi-prepared to deal with the historic mud flow patterns from previous eruptions, No one was even contemplating the effect of the amount of pressure needed to push magma up under the mass of Mount Rainier.
Hard to predict the VEI (Volcanic Explosivity Index) of a Mount Rainier eruption, but in would certainly be one or two orders of magnitude greater than Helens VEI of 5. Think a 1991 Pinatubo (VEI 6 - 10X St Helens) or a 1815 Tambora (VEI 7 - 100X St Helens) in a heavily populated area.
I certainly recall the predictions of mud flows through Tacoma and other areas. The flows caused by Mount St. Helens were scary enough. I wouldn’t want to see that in populated Washington areas. I think there were some that totally wiped out a small city in Columbia some years back.