Salah is likely to continue playing international football at least until he makes the move to Saudi, because it will serve as a powerful negotiating tool for his agent. His ongoing status as a key figure for Egypt, combined with his profile as arguably the most famous Muslim and African footballer in history, will allow his agent to demand truly astronomical wages rather than 'just' obscene wages.
Plus I think he'll just want to. It sucks for it and underlines the importance of starting the league strong and building a gap because we should plan for a drop off in form. The pattern needs appreciating by the club.