Sentence:  Though they obviously realized that these episodes were part of something wonderful and important and lasting, the writers and producers couldn't have imagined that 20 years later “Treehouse Of Horror” wouldn't just survive; it'd <WSD>thrive</WSD> as one of the most talked-about and watched episodes of every season of The Simpsons. 
Meaning of the word marked with <WSD> tags:  To increase in wealth or success; to prosper, be profitable.