I would not prune it back till mid winter. Acers have a lot of sap and the last thing you want to do is cause it to bleed. There is a chance that reserve leaves come out, either way I would wait.

As you know, Acers hate wind, adding a trellis to give it more shelter, or if space, a tree that tolerates wind like Tamarisk and the like.

Thanks, K. I was thinking that would be best, not to prune it till late in the year. Good to have that confirmed. Meanwhile I hope it can recover a bit of leaf on top, as it looks rather odd at the moment.

I lost half of an Acer garnet last year when I trimmed it due to dead branches. It bled sap (I did not see it) and it died down to the roots. The partner branch has stayed fine as it was not cut. I lost an Acer palmatum the year before due to excessive rain (shot drain pipes due to icicles and the whole roof drained onto the poor plant!). Prima donna plants but so lovely at the same time.