1. Any massing of forces to invade Alaska and Washington state would have been seen.
2. Alaska and Washington state did not hold enough strategic value to warrant the committment of vast resources to capture them.
3. The Soviets would have well outstripped their lines of supply.
I'm not going to argue about what could have been, but your post does not conform to the reality of my experience as an army officer at that time.
That is what it is fiction. Its a war game exercise.
I call it the “Red Dawn” scenario.
If I recall, the Penatgon has similar wargame exercises such as OPLANS