It appears that Baker Mayfield could be out of Cleveland even if the team does not end up trading for Deshaun Watson. In an article from Mary Kay Cabot of Cleveland.com, it is specially mentioned that the Houston Texans are not interested in players only picks. That would mean that Mayfield is not part of what the Browns are offering for Watson.
It is apparently not a secret that there is a problem between Baker Mayfield and Kevin Stefanski. The quarterback criticized the play calling from Stefanski on more than one occasion last year which could not have sat well with what was the reigning Coach of the Year. While the fourth-year quarterback did deal with injuries last season, there were multiple non-injury related issues that still have not been fixed.
Additionally, an appearance from Jim Donovan on 92.3 The Fan in Cleveland provided some insight into how things may have been received internally.
The moment the Browns decided to make a hard push to acquire Watson it essentially ended the Baker Mayfield era in Cleveland. But the reality is that it may have been over prior to this, long before the team made any sort of approach to Houston about acquiring Watson.