I think it is fairly simple really. His cap hit next year is 2.709 mil.
If they cut him him prior to June 1st they take a 5.870 mil cap hit. Thus, he wont get cut before June 1st.
I guess they could cut him with a post June 1st designation but that still would mean a dead cap hit of 4.514 mil in 2018 and 1.356 mil in 2019.
If they manage to trade him, and Guru had an excellent idea of trading him to the Browns for Corey Coleman, they would take a 2.712 mil dead money cap hit and then take on Corey Coleman's deal.
Considering that a large number of receivers take until their 3rd year to make an impact, I imagine the Vikings will stick with him at least one more year.
No matter how you slice it though, he has been a major disappointment.