Based on my experience...

"Are all these WAS's just living a pipe dream, or can they truly find happiness so quickly after leaving a long term relationship?"

Pipe dream. Fantasy land.

"How can they detach so completely, that they are totally happy in their new lives? "

They started the detachment phase months or years before bd. They aren't truly happy. It's a phase that won't last.

"I just don't know if that is possible. Is it?"

Not for a "normal" human being.

Me-35 Com law-28
S-3
T-6 yrs w/14 mnth bu
1st bu- 2/2012
Rec-4/2013
2nd bu-10/2013
IC-2 yrs(anger issues)
MC- 5 mnths-fail
OM~1/1/14 OM dumped 6/4/14
New OM ~10/4/14