It could shear off flush with the slave cylinder and still not leak - unless it was leaking before he messed with it.
The mechanic will be able to pop a new brake cylinder on and probably ( hopefully ) only charge about an hour's labour. That will be easier than trying to get bleed nipple out...might be best to get one to take with you to the garage.
Decided to take the advice of new cylinders. After much research I ordered a couple. Only to be sent two different ones by the same seller. Local non-vw mechanics have said, once I get the part, that they can do it. Mostly 3miles of backroad to get to them so even with dodgy breaks I should be fine. Seems the Bleeder Nipples have a tendency to rust within the cylinders. I do intend to bleed the brakes and change the fluid every couple of years from now on, so I am wondering if it makes sense to just twizzle (not enough for fluid to come out, which I read is a 1/4 turn) with wd40 every so often to keep them, and the new cylinders, in good nick? Cheers folks. Sent from my iPad using Tapatalk