The short answer is: it'll depend. It'll depend on the waiver itself and the allegations. It's almost certain the family will allege more than just negligence against CrossFit. They'll likely allege everything from gross negligence to willful and wanton acts against CF. I don't know what state the waiver was signed in, but different states come to different conclusions on what can be waived. My guess is that the family will sue, it'll survive an initial motion to dismiss, and CF will settle. But that's just purely a guess.
Caveat: I'm a lawyer but I haven't been in litigation for about 5 years now.
Also, I think Disney dropped that argument on the wrongful death case. Insane that they tried it in the first place.