What about planting it in the ground?

Not an option at the moment, as I am waiting for ground work and a 3' Cornish hedge to be installed. Repotting will just be an interim measure.

If it can be rejuvenated, it will end up being planted out during the autumn or winter.

ALL rhododendrons have latent buds located under the bark that can be stimulated into growth by hard pruning. I never hesitate to cut back any that have become too leggy for whatever reason (although will do my best to correct whatever the cause was as well). Never lost a shrub yet!!

Interesting, gg.

Nothing to loose, so I will, initially, cut back one of the stems and see what happens.

That is what I planned on doing, anyway.

I did find the info online a bit confusing, with types defined by smooth/rough bark and scaley/unscaley leaves.

Yeah they will actually recover quickly when they are (newly) happy.

I had a 'Wheatley' (sounds like the name of a butler!) that had been planted too deep and in a slightly too damp spot. Probably the last rhodie I planted before I had better mindfulness of those issues in my climate. I moved it in late winter to a slope with much better drainage and it is growing like crazy.