Sharp still would be one of the top five-six forwards on the FA market, so once FA gets into full swing, I am sure a team will be willing to take the entire hit. Of course, they may lessen what we get back on the back end, but with their current situation, they are better getting less back and dropping the entire cap hit.
As for Lucic and Boston having to keep some of the salary, that is what I would have expected if Bowman made a trade on draft night to get a 1st rounder and full value. Since he did not, he should be able to drop the entire salary.