Update: According to Joel Corry, the $600,000 workout bonus for Mike Williams is not guaranteed, which means the Bucs would save that amount by cutting him.
New reports suggest that the Tampa Bay Buccaneers can cut Mike Williams and not be hit with significant cap hits, contrary to earlier reports that said his 2014 and 2015 salaries were fully guaranteed. It appears that only his 2014 salary is guaranteed, and his 2015 salary won't become guaranteed until next year, per Mike Garafolo. Joel Corry confirmed this, and noted that the date for his salary to become guaranteed was the third day of the 2015 league year.
Mike Williams is due a fully guaranteed $1.2 million this year, as well as a $600,000 roster bonus which has not hit yet. It's not clear whether that roster bonus is fully guaranteed, although Jason la Canfora says it is. If cut this year, the Bucs would owe the wide receiver just $1.8 million, which would also be his 2014 cap hit. The cap hit would turn into $0 if someone picked up his contract off the waiver wire, or lowered by whatever salary he'd be signed to on the open market if not claimed on waivers.
Given the team's vocal and public displeasure with Williams, it's certainly possible that they cut ties with the receiver -- even if the only thing he's done wrong in this case is get stabbed, as far as we can tell. Still, cutting Mike Williams would only make the team worse. They're already suffering from depth issues at wide receiver, and saying goodbye to one of their starters (who has been pretty good when healthy) is not going to help matters.
The Bucs have also tried to trade Mike Williams, per Jason La Canfora, but haven't gotten any takers -- presumably as a result of his off-field issues, as his 2014 salary is pretty reasonable for someone with his talent. At this point, a release does seem more likely, but they have effectively the entire offseason to decide on Williams' fate and try to trade him.