I went back to read your orignal post — did you ever find out how long ago he was neutered?
Is he aggressive at all with you or anyone else in the house? And if so, are there particular times when he is? Like when you are changing things around or giving food.
Though it can create a bit of a set-back to have such a nasty fight happen, don’t lose all hope. There have been members like Markus who had bunnies that really just wanted to kill each other and they went through some hard knocks, but they did bond. He did however take them to a rescue (SaveABunny) that offered bonding services and that helped thank goodness, as I know Markus had tried everything.
Have you tried stress bonding? Car rides etc? I’m not saying do that right now, as after such a nasty fight, you may want things to get settled down first– and make sure that no wounds or injuries are hidden somehow.
Another method that may help is the “stunt double”. Basically a toy bunny that has Molly’s scent on it — you can brush Molly’s fur and then take all of that fur from the comb and put it all over the toy bunny. I know this part sounds gross, but you can take the back-end of the toy bunny and put it in Molly litterbox.
Most likely when you put that “stunt double” into Hennessy cage with Molly’s scent all over it, he may attack it, but the hope is that once he finally settles down and gets use to it, he will get used to her too eventually. I used this for Jack because he is so humpy, and he can wear himself out on the stunt double rather than bugging Vivian so much. If he gets used to it, you can make moves with the stunt double — like have it groom Hennessy, have it asked to be groomed. (wear gloves though during this time though!)
Doesn’t mean that Hennessy won’t be upset if he meets Molly later, and she ends up being more bossy than the very passive “stunt double” but maybe he’ll at least give her a chance.
Another technique to protect your Molly when you are first introducing again in a neutral territory is use a large thin netted strainer. I learned this trick from SaveABunny too. With a strainer, they can see and smell each other, but if he decides to attack you can stop it before he actually gets to her. (and wear gloves because you will get bit if he’s ready to fight–and as your husband has found it, bunny bites really hurt. Their teeth can latch on which is how they can hold on with their teeth and kick with their back feet during a fight….brutal fighers bunnies are!!)
By the way: Do you know much about Hennessy’s past?
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