Seeing the Boston leg of the production, I am pretty sure I saw Martha have an orgasm onstage. Which didn't bother me per se, but I did think it was going much farther than it needed to. I posted earlier that I really only had one spot in the show musically that I thought hit the wrong tone - I will add to that that their treatment of Martha in general seemed off.
That said, it IS a song about sex. But then again, so is Yours Yours Yours" to a degree - "my favorite lover's pillow" et al.
As far as the final refrain, I do think the key word is WHEN (Heaven calls to me). I'm not sure I have ever really read foreshadowing into that. Everybody dies, save the Tuck family. :-) In the original orchestration, Sauter brilliantly "underscored" the moment with nothing more than a repeating chime (on died/bride/wife/life).