As I understand it (and I might well be wrong!), if the power is cut to the car for too long the ECU 'forgets' the key code and won't disable the immobiliser when you use the normal red key. You can get around this by using the maroon master key which has a transponder which activates the code system on the ECU and everything is OK again.
So without the master key, the ECU just doesn't recognise the code in the normal key so you are left with a big bill to replace the ECU, keys, locks, etc.
What I really don't know is if you can somehow activate the code system by using the number on the 'code card'??
But to complicate it even more - the 'code card' was never issued to purchasers in the UK as the insurance companies objected for some reason. I understand that some dealers recorded the code on an incomplete database, so the original selling dealer may be able to give you the code? Otherwise, maybe you can get the code from Alfa?
Now, whether you can actually use the code to solve the problem you have if you actually manage to get hold it – I really don't know… but I'm sure it's worth talking to the dealer about in case it saves spending stupid money on new locks and keys!
Sorry about being vague, I'm on fairly dodgy ground here I'm afraid, so I hope someone comes along soon who knows a bit more...