I thought it was a brilliant series, so many twists and turns. I was a bit confused by the ending too, but:
I think Marcus and his wife got away with it because the police didn't know about them. They drove off into the sunset with half a million in the boot.
I think the police didn't know about the warehouse because Chris hadn't been kept in the loop by John. Chris was never interested in the money because he'd learnt from bitter experience crime doesn't pay. His happy ending was to be with his wife and new baby.
John's ending was the hardest to work out but I think you have to remember the first episode when he went to the cashpoint and used his own money to top up the monthly shortfall. I think he wants to be seen as some kind of hero and will make out to the police that he knew the crime was going to be committed and stayed on the inside of the job in order to get the money back. Whether he will get away with it is another matter.