This is from 2019 and I found it while looking for articles for my Federer retirement blog. Tumaini Carayol discussed how tennis would survive without its superstars, namely Roger Federer, Rafael Nadal, Novak Djokovic, and Serena Williams:
What happens when the legends finally retire? This is the question that players and coaches, tournament heads and TV programmers, casual fans and die-hards alike are grappling with. “Oh, wow,” said Judy Murray, mother of Andy Murray and accomplished coach, when asked that same question. “That would be massive. They’ve been around for so long. They’ve been dominant for so long. It would be a huge, huge blow to the men’s tour to lose them for so long.” Feliciano López agreed, pointing out the economic impact that the players have had on the sport. “Because of them, tennis got so much attention. Because of them, tennis got more sponsors, more money for the tournaments and for the players.” Maxim Yanchevsky, a producer for Eurosport Russia, echoed the concerns throughout the sport: “There will be a minute when Federer, Djokovic, and Nadal retire, and I’m sure that the interest will go down. It’s 100 percent. I’m not an expert, but it’s for sure.”
I think the issues are different on both tours. The WTA has been and will continue to be fine in terms of popularity and interest. Świątek is ruling the roost but the players below her in the rankings are all capable of winning slams (and a few of them already have). The ATP will, however, suffer when Djokovic and Nadal follow Federer and that’s down to officials pinning their hopes on those players pulling in the sponsorship money and the crowds. It’s not that the other top players aren’t good—they just don’t have the same appeal. Time will tell if/when that changes and whether the ATP will continue chasing money in bad places (like IMG’s ten-year $1bn betting rights deal).