Suitable remedy for chain damaged by bike shop I've got a fairly old Dawes Discovery 301 (not sure of the year); earlier today I took it to a shop to have a replacement bottom bracket fitted. I rode it 2 miles home, and noticed a slight intermittent skipping feel and noise from the chain which hadn't been there previously. I didn't stop to investigate until I got home as both the noise and the feel seemed "minor" (learning point for me there). When I did, I found that one link on the chain had one side detached with the pin sticking partway out; the eyelet on the detached side is quite bent. I'd attach a photo but my camera has apparently stopped working. It's not an easy-open link or anything else fancy.

I'm concluding that the chain's been re-fitted badly. I plan on returning to the bike shop (not riding the bike!) and asking for a new chain to be fitted free of charge. I can clearly see the lettering on the links saying it's a KMC Z40, which I'm guessing is discontinued because I don't get any relevant-looking hits on a search. It's on a Shimano CS-HG30-81 cassette.

Questions:

1) Is my plan reasonable, or is it well-known for older chains not to re-attach well? I've measured the chain to look for lengthening due to wear (per http://www.bicyclinglife.com/HowTo/ChangeAChain.htm) and I believe it's at most 1/16th out at the 12-inch mark, so I'd say it's worn but not excessively so. The cassette doesn't "look" terribly worn either. I acquired the bike recently-ish from a relative so can't be sure about its previous use history, but I don't think it was massively punished.

2a) If 1) answers "yes", is there any specific type of chain I need to ask for? I ride on roads most days and on light off-road trails on occasional days.

2b) If 1) answers "no", please can you advise on an alternative strategy? I recognise this is subjective and calls for opinions, but I'd be interested to see what others think is reasonable in this situation.

I've used this shop before and always believed them to be reputable.
@Alexander is right, there is no need to break a chain when you replace a bottom bracket. So your hypothesis doesn't make complete sense, unless maybe they were doing other stuff to the bike?

So if you do take the bike back to the shop, odds are that that's their response.

I know if I got myself a new (second-hand) bike, I'd think about replacing the chain almost automatically. Same as something like brake pads. Just so you know where its come from, plus they're cheap enough its almost a no-brainer. 

By the looks of that cassette its an 8-speed, so you just need an 8-speed chain (e.g. http://www.kmcchain.eu/?en/products/multiple_speed/8_speed_derailleur/). Really common, any bike shop will have one. If you decide to buy off the web and fit it yourself (easy enough, just need a chain tool, which is an invaluable tool to have in any case), actually KMC is a decent brand to go for anyway.