I'll have to get someone to quote (will ask neighbours who they have used), for removing the tree, which I think long term will be needed, but I am tempted to go for the RR (avoiding predictive!) in the meantime. I think I have enough space, but it looks to grow huge - would I be able to keep it less bushy towards the bottom? If the tree is diseased is it likely to affect the RR or other plants? At the moment the neighbours over that part of the fence wouldn't even notice it, but future neighbours may get upset if it encroaches on their side too much - how prickly is it for pruning with regard to reaching over the fence to keep their side in check? Just so you know, it would be my first ever rose I have bought! ( got a small multi-coloured one that I inherited with the house but that's all).
When it comes to removing it (hopefully before nature takes it's course), then I'll think about replacing the tree, maybe with the liquidambar as suggested, I should have enough space to dig a big enough a hole to the right. Looking at the garden as a whole a replacement tree would be the right framework/backdrop to fit in.