2010 Mondeo XR5 cooling system question

[PeteBlu]

Sorry for the long post, I want to be as clear as possible.

I have a 2010 Ford Mondeo XR5. Last week the radiator hose blew out, I had a mobile mechanic come and replace the hose (I‘m not very mechanically skilled). They ordered a genuine hose from Ford, fitted it, refilled and bled the cooling system and took the car for a brief test drive.

I’ve done less than 50kms since then, but yesterday as I was driving in town I noticed the car was very slow to accelerate, and I actually stalled it at one point the power was so low. Shortly after that the engine just stopped, I tried once to restart it, unsuccessfully. Pushed it to the side of the road where I discovered that the hose had come away from the radiator (I think it’s that end anyway), taking the flange with it (see image). Called RAA, had the car towed home.

So, some questions:

1. In my mind, this is clearly the mechanic’s fault. When I called him today he admitted it could be, but repeated a few times that it was “fine when I left it”, and mentioned that it was a snap-on fixing. I suspect he’s going to try and weasel out of it. What are your thoughts? Does the hose simply snap on to the flange, or did he overtighten or cause damage in some other way?
2. If that flange has come off the radiator, does the whole radiator need to be replaced?
3. Is the engine likely to be damaged? Hard to answer I suspect.
4. If the engine is damaged, is the mechanic responsible for repair costs?

Thanks for your time, let me know if you need any more info or clarification.