I was descaling my Europiccola... rinsing it with fresh water, and when I tipped i heard a funny clang. The copper pipe is detached.

Well f! What now? Is this normal? Seems to have been "screwed" into a black plastic/rubber piece.

It's a millennium, bought around 18 months ago

It has happened to me ... once. I don't know why, and it hasn't happened since.

only the very early pavonis have their groups screwed directly into the boiler (and shouldnt be unscrewed unless for very pressing matters).

All others have their group secured with two bolts (10mm Hex socket).
if you unscrew those, the group comes right off (might be a good time to replace the sealing O-ring).

Now you should be able to reinstall the dip tube, or, if it has snapped off, take some pictures and report back here.
if it can be pressed or screwed back together, simply do so, and reinstall the group to the boiler.

always unplug your machine while tinkering.

Good Luck, send some pictures!

So I unscrewed the group head, worked the bolts carefully and... They broke off! The bolts and the area around them shows lots of corrosion.

The head is out, but the bolts I'll have to drill out or something. Not expecting it to be easy given the corrosion.

This is a mess.

(I'm a sailor, with lots of great that handles salt water for years with little or no corrosion. The cheap metal in use here strikes me as crazy...)

Local repair shop specializing on these machines says it's risky to drill them out. Argh.

Oh man, thats unlucky.

I guess only way to go is forward...Try drilling them out, and replace with new bolts.

Could you send some pictures?

A good machine shop should be able to get them out. I would be wary of going to an espresso repair place unless you knew for sure they had the tooling to extract them safely.