I’m sorry that you lost your bunny in such a horrible way!
I’ve seen a lot of things online recently about decontaminating after RVHD2. The Rabbit Welfare association has a ‘cleaning protocol’ for that online here (you need to scroll down a bit):
https://rabbitwelfare.co.uk/rvhd2/
I’m not sure how relevant that is to Myxi though…This website says that Myxamatosis will survive in fleas for 4 months, but less in the wider environment, but I’ve not used this website before, so not sure about its reliability.
http://animalhousevets.com/questions-about-myxomatosis/
It might be worth calling a rabbit specialist vet and seeing what they advise. I believe you need a specialist disinfectant too, not just bleach. But it may be that after a year it will have all died off by itself anyway.
I imagine that its sadly also something that rescues are experienced in dealing with outbreaks of, so that could be another option for contacting for advice.