Ok so the first real sunny day has just hit my part of the UK today and as luck would have it I had to go out early & forgot to rewater my lovely Wisteria bonsai (only a year into its pot) and despite watering on my return (when I'd swear it looked fine) 2 hours later I was faced with this

It's been perhaps overly watered since in sheer panic but has only held on to 2 tiny thin stems of leaf that look reasonable. So I'm just wondering if it's likely I've lost it completely or can Wisteria ever cope with such an assault on their roots to be able to push out new growth (if not completely dead obviously)?

It's heading off to a local polytunnel for the rest of the summer to hopefully prevent a recurrence.

Don't panic.
Wisterias need an under tray full of wet pebbles to keep moisture in the summer.
Yes, it is wilting, but now take it to an open shaded place, water when needed, and wait.
It's almost certain it will make it.

BTW, with a good open substrate it is impossible to overwater...

Look at the stems between the leaflets. If those have dried out fully it has had a big hit. If those are succuluant, shiny and green you will probably be OK.

Keep in mind that your plant now will use WAY less water. Overwatering is a risk now. Especially if the roottips died of: It will need a week or so to start root regeneration. So be carefull watering now.

Ahhh guys thank you SO much for all of that encouragement and invaluable advice, esp on the overwatering etc. Yes, it is in a perfect substrate (my local expert potted it up for me - he's just away at present) but I'll keep it in the shade for the week, esp given it's turned warmer now - just didn't want to flog a dead duck so to speak. The strange thing (to me) is that some of the early leaflets have died off almost fully & shown no signs of improvement at all, whereas some of those furthest away from the trunk have held on better, but I presume that's just the luck of which roots nourish which sections.

I'm beyond gutted but know you all at least understand that more than any others I could tell about it!