I have to agree with Becca. If they were suffering then no problem- PTS. I mean in this country we don't even euthanize suffering humans, we only have this option with animals, but i know we certainly wouldn't consider culling a healthy human being just because of unfortunate circumstances and to me a bunny deserves the same chance, even if the ultimate end is suffering then death.
Most animals suffer then die, it's part of the natural process of life as we either decline in health or get eaten by an animal higher up in the food chain. Fortunately for human beings we are at the top so we don't have to go through what a animal who is lower down the food chain does. I think most animals are well equiped to survive.
Every cell in an animals body works to keep it alive, it will run from danger, try get food, shelter- i wouldn't discount the natural instincts of even a domestic bunny. Animals are not truly helpless in the wild, they are just at more of a risk of coming to an end by natural causes, sooner than if they were caged up by humans. I am pretty sure if i was a bunny i'd go for the being released in a quiet nature reserve, rather than being put down.
Again this is individual preference i suppose. I don't think there is a right or a wrong on this subject, it all depends on your values systems and what beliefs you have given yourself about what is right wrong, cruel or not cruel.
Ambience x