New Generation of Kids don't care for that old man named Djokovic who is still dominating. For the kids Djokovic is just an old man of their parents age whom they don't need to care for. They will always prefer Alcaraz or the new champ who will win more majors or even less majors. So no,. 30 wont be required, 25 will be enough.
Don't worry, by that time you will be old, so when you tell the younger crowd of those times that Novak is better then X,Y,Z in 2045 then your view will be rejected/cancelled just like I reject the views of 50-55 years olds who praise Borg over current players, for us Big 3 are great, we don care for olden times players, same way Novak will not be cared for.
Look at the wimbledon 2023, the kids are cheering for Alcaraz, nobody taught them to go against Novak, they just don't connect with the old man.
Saudi is developed as well, what more development do you seek ? Their oil will last at least this century, plus it is not like they will have to cancel Tennis tournaments that are bringing them traffic and tourism. A 5th will not reduce the prestige of Slams, even if Saudi does a U Turn on Tennis in 40 years the 5th Slam could be transferred to other countries as well. See the point is, landscape around us changes a few decades, if a sport is dying then new rules will come into place, new investors will be allowed to dictate terms. Even of the day the whole world revolves around money, the legacy of a sport where people hit back balls is not more important than what the investors and the fans of any era demand.