Jen asked me to do a spoilers prediction list, so here we go! be happy, puzzledhat.
Thea dies at the end of 3x19. My particular bet, it’d be the moment Oliver tried to break Roy out of prison.
The offer Ra’s makes to Oliver is to use the Lazarus Pit to resurrect Thea if he accepts to be his heir.
Ray and Felicity break up or at the end of 3x19 or the beginning of 3x20 because she decides to follow Oliver whatever he goes.
Actually, my bet is that Felicity’s dilemma is not breaking up with a guy because she’s in love with an unavailable guy, but rather if she'd leave Starling City, leave everything behind to follow Oliver. Her choice leads her to go to Nanda Parbat with Oliver and that’s the big emotional scene in 3x20 in the jet. It won’t be something as simple as an ‘I love you, Oliver’.
Nyssa will try to take over The League, maybe enlist Oliver to help. Meanwhile, he plays the part of being the Heir.
The wedding is probably a contractual clause to be the Heir that Ra’s will throw at Oliver. My guess is a character that appeared on Arrow Season 2.5 comics. LBR, the writers made arrow a rip-off of Batman, they’ll pull something like this. (worry not Olicity fans, I’m sure even if Oliver gets married, it’ll be obviously a paper only thing and Olicity will remain together)
Olicity ends up this season together and in a happy note.
