Leonard gets the opportunity to go on a four-month research cruise for Stephen Hawking. He's concerned how it may affect his relationship with Penny, but she encourages him to go. Meanwhile, Raj pushes Lucy to meet the rest of the gang, but his eagerness threatens to scare her away.
Leonard's departure was not the big, season-ending cliffhanger. Leonard and Penny's bond, solidified this season, should prove strong enough to handle it. The cliffhanger was Lucy's breakup with Raj. In the aftermath, Raj discovered he could talk to women while sober, leaving him optimistic about patching things up. I hope he does. It would be one of the bravest things he's done; it would show how special Lucy is; and Big Bang will have expanded from a show about four friends to a show about four couples, each with dynamics as nuanced as the characters themselves.