Yeah, no denying it will dent Sony, the question is by how much. Call of Duty sells 15+ Million on Playstation consoles annually, to expect all of these players to switch is unrealistic, but 10+ Million leaving is a real possibility.
One wildcard for Sony, however, is the chance of having the next big multiplayer hit from one of their internal teams or partnerships. Deviation Games, for example, is made up entirely of former Treyarch devs. Naughty Dog's standalone TLOU multiplayer game, an IP with a universe and gameplay mechanics ripe to make a breakthrough in the multiplayer space, also has a television series releasing later this year, could be the premiere multiplayer game that softens the blow of losing Call of Duty.
Sony has a lot of multiplayer titles under wraps, significantly more than the PS4, there's a good chance a few of them end up being successful. They might not be the next Fortnite, but having success similar to Rocket League, Genshin Impact, or Destiny, would be huge for the Playstation ecosystem going forward.