My wardens were kinda all over the place when it came to the Dark Ritual. Some grudgingly accepted it, some flat out rejected it and others jumped at the chance to bed the witch. (Bear in mind - Loghain never survived any of my playthrough so he has no effect them)
My Human Noble (Female) was in a romance with Alistair and had him do the Dark Ritual (So sorry Ali!). I also have two saves where they don't do the ritual and both die taking down Archdemon.
My Dalish Elf (Female) wasn't in a romance with anyone Tamlen and refused the Dark Ritual, made Alistair King and killed the Archdemon. (This will be the first playthrough I import into Inquisition)
My Dalish Elf (Male) was in a romance with Zevran and accepted the Dark Ritual. (He and Alistair stayed with Grey Wardens)
My Human mage (Female) didn't romance anyone and refused Dark Ritual. Both saves, each one dies. (Stays with Grey Wardens)
My Human Mage (Male) was pretty much power hungry and accepted the Dark Ritual purely so he could have a powerful child. (This should be interesting to import...) He makes Alistair King.
My Noble Dwarf (Female) romanced no-one and refused Dark Ritual. Both die. Both stay with Grey Wardens.
My Commoner Dwarf (Male) romanced no-one and accepted Dark Ritual. Both stay with Grey Warden.
My Elf Mage (Female) romanced Leliana and refused Dark Ritual. Alistair dies. (sorry buddy)
My Human Noble (Male) Romanced Morrigan and accepted the Dark Ritual. There are two saves where he doesn't and both he and Alistair dies.
However - I am far more curious about the slides that says Morrigan was pregnant with the Male Warden's Child (if in a romance with him) despite not accepting the Dark Ritual. Morrigan even confirms it herself in Witch Hunt DLC that they have a child together(?) Would that impact the storyline in some way?