They won't hold onto it. Come training camp, if a deal hasn't arisen, they'll send 'Sheed and $3M to a team that's under the cap. Some kind of exchange of second round picks, as well, so that they net an additional pick. 'Sheed retires, takes a couple million, the other team keeps a little cash and gets a pick. We get back a trade exception with a twelve-month expiration.
IF 'Sheed is on the roster come opening night, it will be because he has changed his mind about retiring - but I don't see 'Sheed changing his mind.
Only reason I can think of to not do this kind of trade NOW is that we can trade 'Sheed now for his salary +25%. Pretty sure with a trade exception, there's no +25% when figuring the salaries.
Too many dollars - salary and lux tax - to *not* get rid of 'Sheed before the season starts.