Allegedly he's been sacked because he refused to take a pay cut from his £25k/week salary in light of him being responsible for his own injuries and not being able to play for 15 months.
The other two players have been fined (and have prosecutions to deal with) but can play because they're not injured.
He wasn't driving, however much he'd drunk, the driver is responsible. You could argue contributory negligence at best for getting in the car. The message here, loud and clear from Derby, is do whatever you like, just don't go to prison and you're good to go; someone else injures you, take a good long look at the gutter
And the flip side is he turned down the club provided car to get him home, chose to get in a car with someone who was drunk, and chose not to wear a seatbelt. Avoiding any of which would have likely avoided the same severity of injuries.
Players are ultimately responsible (regardless of how drunk they are) for their own actions in situations like this, they're banned from doing sports like skiing or downhill mountain biking for similar reasons.
Ignore the rules and screw up your knee ligaments whilst skiing when you shouldn't? Breach of contract and no compensation for you sonny.
If he chose not to wear a seatbelt (even when drunk) that'll be all the contributory negligence on his part the club's lawyers will need.
But, yes, lawyers will be making lots of money out of this. 1.25 years at £25k/week is over £1.5m at stake.