As regards re-planting I would suggest perhaps Ceanothus 'Skylark'. I would remove as much of the soil where the rose was growning (within reason) and sprinkle 'Rootgrow' in the base and sides before bedding in the new shrub with suitable compost. Perennials can also suffer so perhaps wait and see if they surcumb. Any future plantings in the vicinity could be treated with 'Rootgrow' just to be on the safe side. Then give all of them a good feed with something like Vitax Q4 in the spring.

Since this fungus might be in the vicinity for quite a while until it leaves and or is removed from the area might I suggest that you place a potted climber at the foot of the post as a temporary measure. My very poor suggestions would be Clematis or morning glory. I suggest these because they grow fast and will provide a full covering over the bare post. This way you will have time to decide on a good perennial that can be safely planted in the ground again...perhaps a different variety of rose that will do much better than the previous one.

As an afterthought, perhaps Sophora microphylla ‘Sun King’ could be trained up a post. It would seem that it has a better resistence to Honey Fungus than Ceanothus 'Skylark' but not so attractive.

I wouldn't put anything permanent there for a year or two just in case the honey fungus is still active underground. There would be growths like bootlaces under the soil.
Lots of useful information here https://www.rhs.org.uk/disease/honey-fungus-managing-outbreaks

It depends which species of honey fungus it is. I have one that doesnt have 'bootlaces' and basically finishes off the sick and dying. Nothing else in the garden has been affected. why not send a sample to the RHS so they can id it and then you will know what you are dealing with.

Hardy geraniums shouldn't be affected by the fungus.

Thank you for all these informative and constructive ideas. I have a lot to think about now! I'm pleased to find that some honey fungi are less lethal for surrounding plants, however, it looks as though a potted climber might be the best option for this year at least.I will certainly send a piece pf the fungus to the RHS as well, and look up the links you have given me/ Thanks again!

I recommend contacting the RHS first to get mailing instructions so a sample can be sent to them in a safe way and in accordance with their mail handling protocol. Remember they get hundreds of samples in envelopes and containers not knowing what is inside of them. Working in that kind of mailroom can be very stressful.

Thanks Loosestrife, will do!