I believe that Jesus’ entire life was one of irony and paradox. If His followers had comprehended the reality of His ultimate sacrifice, I am certain that His followers would not have been in lamentation at all. At the same time, go figure, His followers were still halfway in the world of materialism and in the sense of wordiness, Jesus was being degraded. It was the material, physical degradation that they lamented.
I would probably not go that far. It is human nature to mourn. When my wife passed, I knew, deep in my heart that she was bound for glory in the arms of Jesus. That does not mean I didn't (and still do) feel sorrow in her passing. She is missed regardless because of the hole left in my life. I would imagine the same would have happened with his followers. Even if they fully understood what had happened, they would mourn. We mourn for ourselves more than the departed. It seems to be how we're wired, even when we know better.