I'm thinking this season but it won't enough to relegate them. I maintain the Premier League will punish them just enough to be considered a punishment but not enough to be majorly significant. They'll get fined around 30 points at some point in March or April which won't be enough to relegate them and they'll probably finish the season on around 45 points. The Premier League will do it purely because they've already won the last 3 and won't be stripped of them and in order to sell the league as one where "anyone can win unlike Bundesliga" etc.
City could end up out of the Champions League but it's also probable that they win it again and end up qualifying while finishing 15th in the league. Even if that doesn't happen they'll iron-clad most of their contracts and you'll see very few departures of note.