I see this falling to Roy. Roy has a connection with her already, and he knows first hand what it's like to have a murder you unknowingly committed kept secret. Will he keep it from her? I think felicity will because Oliver told her how he felt she shouldn't know. But I think Roy's own personal experience with it, plus how he feels about Thea...if Oliver is "dead", I have a feeling Roy may tell all. The whole thing. Because he never wanted to keep secrets from her and she is decidedly not safe already since she's in cahoots with Malcolm.