If Liverpool loses to Salah and Mane together, their attack will be completely broken. Although Liverpool is a stable team, but still they rely heavily on these two players. So I don't think they will decide to sell these two players together. Despite the decision to sell Sadio Mane, Salah will probably be seen in Liverpool's jersey for a few more seasons.
Mane and Salah have been Liverpool's two main players in recent seasons, it is clear Liverpool will lose a lot of strength in attack if both leave together in one season. Salah and Mane have stabilized Liverpool's attack during this time, and if both of them are no longer in Liverpool uniforms then I believe Liverpool's attack will be a bit chaotic and not as good as the last few seasons.
I also believe that Salah will not be following in Mane's footsteps any time soon because Liverpool still really want this player to stay for the next few seasons. So whatever it is, Liverpool must be able to convince Salah not to go anywhere even though sooner or later he will be replaced.
I do agree with you that two players must be retained even though Liverpool have strikers Jota, Diaz, and Firmino but I'm not sure if three of these players can be like Salah and Mane of course we won't think it's a bit of a mess if there is a second departure, whatever some of their rumors can still be maintained as long as the Liverpool manager can convince him.
Of course sooner or later they will be replaced but for several seasons it needs to be maintained again so that Liverpool can compete again in the EPL, especially the UCL, of course, there will be many doubts if they leave Liverpool will not be stable.
Yes, if these two players leave Liverpool at the same time, it will certainly cause a major disruption to the club’s offensive system, despite the presence of Firmino and Diaz, so the Liverpool club must preserve Salah and not allow him to move to another club by negotiating with him about the costs he needs, perhaps Liverpool club management will succeed in persuading him, this is what we hope.