I don think any team will quit until after the post 2020 concord agreement has been agreed.
If Liberty media change the way money is handed out and caps costs then it could be a very profitable business owning an f1 team (unlikely but possible) so don't see many decisions for a while yet.
Joe Sawards post from yesterday looks more at the costs side and potential entrants.
https://joesaward.wordpress.com/2017/07/24/strategic-thinking-2/