Jim has said that the Whampire sex-mojo interfaces badly with the WK-mantle's sex/violence/territoriality thing. Things rapidly spiral out of control; it's more than the two "adding together," it's more like they multiply one another.
I expect only one of them would survive the attempt to consummate the marriage.
One resolution that seems possible: the MirrorMirror story will see the Harrys swap universes, and it'll be MirrorHarry (without a WK Mantle) who marries Lara and consummates the wedding (likely becoming Lara's thrall).
I remember seeing that sex with the Winter Lady would likely kill one of them, but I don't remember their being a corollary for other beings of power. But I'm willing to listen.
As for the marriage, I've theorized all along that Harry and !mirror!Harry swap just prior to the ceremony saving Harry from the marriage, but not from the aftermath of everything !mirror!Harry screws up in our version of reality.
