in the 8th season did everybody know it was the final season?

They were originally going to quit after the 7th season, but Penny had a dream in which it was told to her to go one more season... so they did.

~~Lavenny

Are you serious or just joshing when you say that they went
one extra season 'cause Penny had a dream?
Just wondering.

Yes, I'm serious! Odd as it may seem, but Betty Garrett said on the Entertainment Tonight: Secrets From The Set special that Penny had a dream that told her to go one more.

At the end of the seventh season, they shot either two different episodes or two different endings to the last episode of that season. (Not sure which.) One ended the show and one left the series open.

~~ D.