It's hard not to be fearful when we are losing such great players. But I understand where you are coming from. In Pep we trust.
Txiki and co are often in a bit of a ‘damned if they do, damned if they don’t’ situation on here.
All players will move on at some point and need to be replaced (either like-for-like or with a different type of player to allow for a new style of play or new tactics). And at a top level team like us—now demonstratively the very, very top level—you can’t have two world class players at every position, because one of them (or both) won’t be happy playing half or more the minutes they would elsewhere (which is likely the case with Walker; also see Cancelo, aka ‘when you accidentally bring in a slapped Arse’), especially as they near the end of their careers.
If our management wait until the players are past their prime to let them leave and find suitable replacements, fans slate them for being too slow to pull the trigger on a revamp and weakening the team (and chances for future success) by carrying deadwood.
If our management allow players who want to leave to go out for reasonable deals (especially ones at the wrong edge of their prime), whilst looking to bring in younger replacements (or decent, older stop gap talent to allow us to promote and blood players from the academy, which also has demonstratively the best talent in the whole of England, and arguably Europe) they’re slated for letting players go too early and weakening the team.
All the while, they are trying to realise the best strategy of letting players go when they want to leave and when it makes sense for maximising future success (which is more than just the next season).
And no matter how successful we are, no matter how much we win, no matter how many truly world class (some the best that have ever played in the PL, or any league in the case of a few), no matter how many times fans are proven wrong with their fears about incoming players (Yaya, De Bruyne, Gundogan, Ake, Rodri, Grealish (I hold my hands up there), Akanji, etc.), they won’t get anything but criticism and the chicken little riot from some supporters.
I feel for Rodri when he retires — who would want to be Txiki? ;-)