Salah's age is only 29 years old. It's appropriate that he wants to get something new from Liverpool including his contract. With his current contribution it is natural. A salary increase will probably hold him longer, and most importantly he won't leave on a free transfer that will hurt Liverpool. Klop will feel a headache if Salah leaves, it will add new problems. They just need to add new players.
It doesn't make sense to let Salah go on a free transfer and I think Liverpool should put a lot of effort into Salah's contract, but of course I don't expect him to demand too much of a salary. Salah is at the peak of his career, so maybe Liverpool should follow his whims a bit especially regarding salary.
Maybe Liverpool have nothing to lose if they agree to a salary increase for Salah because basically Salah's performance has made this team get a lot of success this season. To be honest, Salah is the best at Liverpool at the moment for me.