I hope they've not gone. I've not used them for a while because my current car is in warranty & I don't want to give Alfa Romeo an excuse to wriggle out of potential warranty or goodwill claims, but I used to use them regularly with my previous Fiat Stilo & Punto & they were brilliant. I never had to return because something hadn't been done correctly or any of that other nonsense that often goes on with garages. Couldn't rate them highly enough.
On a brighter note, their website is still fully functional and doesn't say they've closed, so maybe they're ok?
It seems Mellors of Challow Fiat are now a general servicing garage rather than Fiat specific, so if Palmer & Philips have closed that leaves nothing other than main dealers in Oxfordshire, unless Solo Italia are still going, but they've changed names and moved once or twice so not so sure about them.