Facebook, Google held out, while Tumblr sold, all to Yahoo.
Recently AOL sold to Verizon for $4B while 15 years ago they were buying Time Warner for $180+B
Groupon could have sold to Google for $6B; today's market cap is $4.5B
There's no answer to this question; hindsight is 20/20. Congratulations on building something that someone considers valuable enough to want to buy... that is a feat in itself.