The thing is... Cairne died in a quite obvious way, and there is no easy way out of that. Magni turned to stone in a mysterious ritual from the Titans, that's... I don't know... less dead? to me.
I would love Cairne to be back (even more than Magni), but as wrong as his death felt, that would feel even worse for me. What I would like is something like a spirit warrior around Thunder Bluff helping/protecting his people... and that turns out to be Cairne. A little like that Taunka-chieftain in the Storm Peaks in that quest about the Storm changing history, who still watches over his people? I would love that.
I could even imagine something like that for Magni too, like he becomes "The Voice of the Mountain" and gives his advice to the dwarves, but doesn't actually return to being "flesh" again.