As far as the season goes, let's wait until they actually play some games to see how big of an affect this will have. Hernandez has definitely ruined his career and life, though.
Not only should Hernandez have known better, but his "friends" should have known better too. Hernandez was their passport to things they would never have access to: Hanging around in a million dollar house, going to clubs/parties on his dime, meeting other athletes or celebrities. His friends should have realized that none of that happens without Hernandez and keeping him out of trouble was a priority. At the first hint of trouble, someone should have been in his ear saying "Think about what you could be throwing away" even if that was for completely selfish reasons.
On top of that, none of these "bad influences" or "gang members" apparently had any idea how to cover up a crime: Leave the victim's body within a mile of the house, leave a rental car registered to Hernandez at the scene, destroy electronic devices whose data can be retrieved offsite. I'd hate to think of what plans they rejected before settling on that one.
Bad enough to hang around with criminals. Hanging around with dumb criminals when you're not a genius yourself is, well, we're seeing it unfold now.