Salah's replacement has to be found very quickly. He is not going to give his service for much longer to Liverpool. and he has been one of the most important players for Liverpool. So finding a true replacement for him should be one of the most important tasks for right now.
Actually one of the things that affect most clubs is lack of planning, though in as much as they would already have all the kind of players they needed but planning ahead of time is always one of the most important thing because majority of clubs has been going through a lot because of the inability to have put things in place, so actually just like you said since Mohammed Salah is the most valuable and the most experienced player in Liverpool what the team management supposed to have been doing is to be striving for a good player that would replace Mohammed Salah because already the club management knows that Mohammed Salah will not play for Liverpool till he retired so working on those things now should be there number one priority because if Mohammed Salah leaves the club without any replacement Liverpool will seriously be affected before they would get use to it.
How do you know the club is not making plans ahead for player that will take up Salah's place if he decides to retire today or leave the club. Every club is always looking ahead to know what their fate will be if certain variables changes. As it is today there is no news that Salah is leaving Liverpool this summer, so while will the club bother about that at the moment. That doesn't mean the is not scouting for players that can possibly take up his place in the future. A football club can never be stranded, there will always be players that are ready to fill in any void that may come up in the future. Just look at how quickly Liverpool got a manager to replace Jurgen Klopp, and that goes to any player and staffs of the club that may decides to leave in the future. Efforts are always going on behind the scene, but the club can't reveal their moves until when they deem it necessary to bring it to the press.