it has been said many times (although different people haven said it in different ways)
"the past has happened - there is nothing you can do to change it, and no amount of mourning will affect that eternal fact. You actions will only affect the present and thos actions in turn will mold future possibilities available to you. The only thing you can gain from the past"
While it is a tragedy that you're friend has died so young, it is an unfortunate truth that he will never live again. However, the greatest tribute you can EVER bestow upon him is to take what experiance you have gained from his interaction with your life and use it to possitive effect.
If you remember his teachings and use them wisely, you will never forget him
and thusly he will live forever in the one place most sacred - your own heart and mind