"You have to set up the ritual beforehand—part of the reason why she couldn't bring back Miss Makinami, I'd assume." Because, at least in Strange's mind, Mari is straight up dead. "The only thing required on her end was some of my blood. As for how I negotiated it, I pointed out a list of facts as to why it would be beneficial to bring me back from the dead."

Said list of facts mostly involved pointing out the fact that the Ringmaster has like five nightrunners to begin with so might not want to lose one of them, he has duties to get back to once he finishes his contract, and that Childermass would probably make some Very Dumb Decisions of his own were Strange to actually bite the dust.

"Thankfully, we arranged the contract before my mistake with the summoning." He's not entirely sure how no take-backsies would work with regard to bringing someone back from the dead (and probably isn't even aware of the concept of no take-backsies in the first place, what with being an only child with a horrible father) but at least in Strange's mind, once an agreement is made, then one has to follow it's terms. And the Ringmaster, for all her eccentricity, at least seemed to view things the same way.