One: of course the potential loss from a divorce is often not equal for both partners, meaning on some level they may - to your own point - be unequally incentivized to prevent a break-up.
Two: In some unfortunate situations it may not matter if you try even harder to prevent a break-up if your partner has made up their mind. Or, if you stand to lose more, concessions can be squeezed out of you in an unfair way. Obviously you do your best to avoid a partner that would do anything like this, but in the end you can't be sure for a variety of reasons.
That's a good point, and not something I'd thought about. Perhaps as I'm not very wealthy, these questions are so hypothetical that they sound a bit ridiculous to me. If I had a £200 million in the bank I might be more inclined to worry, no matter how in love I was. More money, more problems!
I would turn your question around. How much does your potential loss from an event affect how hard you try to prevent it from happening? My guess would be the greater your loss, the harder you'll try.
When in the midst of what feels like an irretrievable situation, knowing that you stand to lose economically can make you go back and work on it - and that's usually a good thing. That's my personal experience, but I'm sure it's not true of all people in all relationships at all times.