We at a Northern UK friendly airline deny carriage on a regular basis, this is well managed at our own handling bases prior to the passengers even getting to the aeroplane. Odd ones slip through the net, it’s inevitable as booze takes a while to get into your system. You might have just downed a load of spirits as you pass the gate agent and be perfectly fine, 1/2 an hour later by the time everybody else has boarded and you are getting under way that alcohol has go into your system and you are now drunk.
As for the question - I think 2 years is fine, but they should be pursued by the airline for the costs incurred, again this is something that the Friendly Northern Airline actively does.