I don’t think a fight through the bars means that they wont bond, I’ve heard lots of stories where bonding has worked in spite of a fight.
First things to consider is how long ago they were spay and neutered, its advisable to wait at least 5 weeks after spay/neuter for hormones to die down befire begining any bonding or pre-bonding.
In some cases its best to separate the buns for a couple weeks out of sight and mind to let them cool down.. However that is usually in the case of severe fights and given this was between cage bars it was possibly not actually that severe.
Given the fight happened through bars theres a few things you could try. Firstly, pre-bonding is very important for most pairs, have them housed side by side but not sharing a fence as you have pictured in the photo, you may house them like this for 2-4 weeks depending on their behaviour, do scent swaps i.e swapping their toys and blanket. Feed them together in sight of eachother so they can become calm in eachothers presence… They should eventually get used to eachother. Swapping which side of the habitat they are in every day or so can help, although I have not used this method before but only because my boy goes insane if you pick him up and takes a few minutes to actually catch… So it might not be worth the stress to them in certain circumstances but if they will allow you to pick them up definitely try it.
You should notice them calm down overtime hopefully, they should start flooping together (which i see they are in the pic), mirroring eachothers behaviour such as eating hay at the same time, using the litter tray at the same time.. all positive things.
Some buns are just super territorial in their spaces and end up behaving completely differently when bonding in neutral space.. My previous female Bella would strongly guard her territory but ended up bonding with my boy and being very loving.
Bonding is super stressful and can be lengthy but the majority of pairs do work! 🙂