The problem here may be getting your wife to do anything at all, if she's "happy" with things as they are why would she change or try anything else?? You can guide/suggest but only she can act!!
I get the feeling that you still love your wife (otherwise you wouldn't stick around & you wouldn't care etc). Are there any support groups for family members of people with mental health issues near you? This could help you find out what's available in your area & what others have found useful that you might try in order to get your wife to act!!
How old are your kids, could they be co-opted to help you help your wife??
Would your wife take some "vitamins"? There are some natural medications like 5htp (tryptophan), sam-e, vitamin b's, dhea, that can hep or even overcome many mental health issues (every one is different) these shouldn't interfere with any meds your wife is on & she might be willing to take them on the basis of general well-being/general good health (i know it's not totally honest but sometimes backdoors are necessary).
Many meds lower or totally eliminate your sex drive whereas the natural ones do not do this especially dhea (it can actually increase sex drive, emotions etc).
Could you talk to your wife's dr about where you are at & whether he/she feels that it would be detrimental to your wife to talk to her about your feelings & the fact that you feel your marriage to be on the line?? If your wife really knew this it might give her enough of a push to do something.
Is there anything you & she or all of you as a family enjoy doing together? Is she interested in anything? Getting her doing things that are positive might also help, giving her positive feedback when she shows positive emotion or interest in things could help too. Most of us respond to positive input (even if it takes time before others see that it's worked) - this is an area that the kids (if old enough) could really help with, the maternal instinct can be pretty strong.
Good luck