The chance that Graham stays is real. However there is a possibility the Saints will have a problem with the cap, they could decide to go a different way, or they cannot come to a deal with Graham in which case they will franchise tag him.
Like happened to Chris Ivory (tendered, not tagged) I could see Graham being tendered and then being traded. If you got this huge value guy that is going to be gone/worthless to the roster next year you might want to get something back for him.
Is a trade reasonable? Yes. Is a trade unreasonable, also yes! Any team with cap space would like Graham on their team (the reason part). The Browns on the other hand… they might want to get Graham for an unreasonable price.
Last year Percy Harvin (by far not the superman Graham was/is) was traded for a 1st (#25), 4th (in 2014) and 7th round pick. He was an injury bust. Though this might caution some to make a trade like that again, the guy who allowed Ditka to trade away all of the Saints draft picks is now the Browns' front office, so anything is on the table.
What would you like to trade Graham for? Name your price!