“Eh, this could be handled”
True. Mount Rainier is not an explosive volcano like Mt. Saint Helens - or Yellowstone. It would heat up, lava over the top, melting the glaciers and causing a lahar that would travel down the slopes at high speeds. In the past they have been tens of feet thick and have reached Puget Sound near Tacoma. Would be a real tragedy and lots of lives lost and heavy damage. But yes - it would be handled.
Yellowstone would kill off a huge number of people worldwide over the years by destroying the breadbasket of America that provides food worldwide, and also cooling our climate for years and years limiting worldwide crop production. I don’t think it is an extinction type event, but perhaps 1/3 to 1/2 of humans would die????
Mount Rainier has had explosive eruptions in the past.
Nobody can predict a volcano’s behavior. Even Kilauea had an explosive eruption back in 1790.