Yes, unless he pulls a Brett Favre, whereupon he comes back, is bought out (or released), then signs with another team. Alexander did not get all of his money from Seattle as he did not retire. He was released by the Seahawks and subsequently signed (and as of today released) by Washington.

they only get the money they earned that year.
example: 4 year 8 million dollar contract, retire in 2 years. you get 4 million dollars plus whatever your bonus is.

The team is off the hook for the salary. I think they still have to pay part of the Signing bonus tho.