But what do both marriage partner's original religious and/or civil marital vows to one another have to say about this?
Are they not worth so much as either the paper that they are written on, or the breath which they were confided to one another with?
While I generally agree with much of what you say as I am very pro-marriage and preserving a marriage if at all possible, I slightly disagree here. I am nearing 70 and have seen a lot in my life. I have learned to forgive a lot.
I am also a big fan of David Schnarch and his views on marriage. He believes that marriage if done correctly is very very hard. He views every aspect of marriage a balancing (negotiated settlement) between the husband and wife over one partners high demand and the others low demand. This includes sex, how often to have chocolate ice cream for dessert, and what and how much TV to watch.
Schnarch likes to point out that the hard part of marriage is that it involves two individuals that mature and emotionally change over time. This creates a constant push/pull between them as they grow and evolve at different rates. He views the hallmark of a good marriage as the ability to self-differentiate and grow to become true to your core values and the best you, you can become. Another is to self soothe, so that those things in life you find are holding you back or gridlock issues with your spouse, you can find a way to relax about them, try them and figure out if you can just get past your fears/revulsion etc. Finally a good marriage is about negotiated compromise between spouses.
Now to the point. (Sorry for the digression.) The original marital vows were the negotiated agreement at one point in their life. If they still represent both of their core values and/or boundaries or even if they still represent just one of the parties core values, you are right.
On the other hand, if because of illness or other circumstances, enforcement of the original marital vows would cause more harm to the relationship/marriage, then maybe they can renegotiate and self-soothe so that they both can live happily ever after.
Would I prefer if the wife could self soothe and figure out a way to satisfy her husbands needs. Sure, I am sure she would as well. It sounds like for some reason she can't. It sounds like she wants him to be happy. It sounds like they both care about each other and want to stay together, so I am not going to judge them.
As I look to the future of my marriage, I know that as we age, one or both of us will have health issues. Some of those issues could make traditional PIV sex impossible or very difficult. As we get older our definition of sexuality and intimacy will change. I have been with my wife for 46+years and hope to be with her until I die. Change can be frightening. I hope that my wife and I can work through our fears, physical changes and stay emotionally close. We have been through a lot and found so many shared values, beliefs and goals, that I trust we will be able to work out whatever comes our way.