I agree, t-p. The ending is so unlikely that I feel it weakens the opera. He'd have done better to make it a total stark tragedy.
Jenufa was the first opera I saw and being a slightly nervous soul I got to the theatre about two hours early - I didn't realise I had a ticket for the pre performance talk but was lucky I was so early and that I was there for the talk.
The guy who did the talk basically said of the ending: don't try to rationalise or understand it, everything is in the music. It is pure 'opera' in that sense - emotional and not easy to explain.
I'd go along with that. And also both productions I've seen (WNO '98, ENO '06) have made the ending plausible at least - through music and action.
(I realise this post may make no sense at all.)