Depends on whether the artist "owns" themself. If I go to a Harry Styles concert and the guy is unable to perform on the stage, I should get a refund, the corporations behind Harry Styles failed to deliver a product. If I go to a Marc Rebillet [1] concert, well, I know exactly what I am getting even if Marc is barely able to yell 3 times in the microphone (and those screams would be exquisite anyhow).

[1] https://www.youtube.com/watch?v=sytXwAvAdL4