Well it probably won't happen, but Jayne wasn't casted. Untill they actully say characters name in episode, or character gets some defining action (like Tommen, being blond and at the same table with Lannisters) they don't count. Because they can (and will) recast them. They also need someone who can do nude scenes (if they chose that direction, we still don't even have Ramsy so we cannot know, and what will Theon do for like 2 seasons.). There is a question how will they introduce character of Jayne (probably Littlefinger just randomly finding someone who we are told is Sansa's friend Jayne?). Maybe they will send Jayne Westerling (Lannister?) but i don't know would I like that. Most likely, because of how D&D reacted to question -is that girl in season1 episode1 Jayne Poole-, they will just "recast" her and go that way. They changed Asha to Yara because its close to Osha. And they will have 2 Jaynes, unless they change something again. Sansa mentioned "Jayne Poole's mother" in season 1. Interesting question, is Ros going to have a full, new story arc now? Whose roles will she take over? What part in Littlefinger's plots will she take? I can't imagine her just earning him money.