Y61 high pressure fuel pump fail

[Boyo]

I have been advised by the Nissan specialist in the UK that the high pressure fuel pump has failed. The history to the problem starts like this, I parked the car in a neighbours yard for safe keeping, it was we thought out of the way but they needed to move it and up to that point had always been a good starter. They tried to start it (without waiting for the pre-heater light to go out) and it wouldn't start, the battery ran out of charge. I on my return re-charged the battery and waited for the pre-heater light to go off but still no start. I got a mechanic from a local garage to see if he could get it going, he tried pushing the priming plunger on the pump under the bonnet numerous times but no start. now the Nissan specialist says the pump has failed and it is very expensive to supply and fit and program to the engine, £4,800.00, that's an awful lot of penny's.
Why would a pump just fail, what could have happened to cause it to fail. I can only take the garage's word that that is the problem, should I ask for diagnostic codes to verify.
I think I may have found a company here in France that can supply a re-con unit much cheaper, would it be worth it if the garage will still fit and program it?

Any help and advise would be most appreciated
Cheers
Boyo.