Forum:Gravekeeper's Descendant Priority

Me and my friend were having an argument about Gravekeeper's Descendant's effect.

Player A: Summons Gravekeeper's Recruiter, and chooses to activate the effect of Gravekeeper's Descendant (which was already on the field). He sends Gravekeeper's Recruiter to the grave in order to pay the cost and resolve the effect.

Player B: Activates Compulsory Evacuation Device, targeting Gravekeeper's Descendant.States that Descendant's effect will no longer be able to resolve as it is not on the field, and also claims that Recruiter stays in the grave.

Player A: Argues that a trap cannot activate in the middle of the activation of an effect and that the effect of a monster will resolve even if it is no longer of the field.

So what should actually happen here? Will a card on the opponents field still be destroyed, or will have Recruiter been sent to the grave in futility?

THANKS