I was thinking more along the lines of the legal engagement, and that he is not allowed to end it. I suppose if there were some public exposure that yes, he would be found to be in the right.

I don't think he's that bright anyway. I've just read some posts this morning that point to the idea that he could have brought things to a head by confronting Maria or Mr. Crawford, or both. And that in turn might have caused Maria to break the engagement. So yes, I suppose he could have done something.

I went back to find his feelings for Maria and all I found was this from ch. 4
Mr. Rushworth was from the first struck with the beauty of Miss Bertram, and, being inclined to marry, soon fancied himself in love.

Are his motives selfish in wanting to marry Maria just because she's a beauty? He fancied himself in love, but did that wane as he watched her gallivanting with Henry? I see now that he probably could have negotiated a release from the engagement, but he's a bit of a chump isn't he?