Cris,
There can be no sacrifice if nothing is lost or given up. If he gave up his life not knowing if he would ever come back then that might have some meaning, but he was omniscient and immortal so he knew exactly the outcome. This is like saying you struggled hard at a difficult exam and passed but you knew the answers in advance. Again with omniscience he would have just been following a script, and his actions would be as meaningful as any soap opera.
God's omniscience is limited by our free will, in our own choice. Jesus had a free will in the garden:
Matthew 26:36-46
"36 Then Jesus came with them to a place called Gethsemane, and said to His disciples, "Sit here while I go over there and pray."
37 And He took with Him Peter and the two sons of Zebedee, and began to be grieved and distressed.
38 Then He said to them, "My soul is deeply grieved, to the point of death; remain here and keep watch with Me."
39 And He went a little beyond them, and fell on His face and prayed, saying, "My Father, if it is possible, let this cup pass from Me; yet not as I will, but as You will."
40 And He came to the disciples and found them sleeping, and said to Peter, "So, you men could not keep watch with Me for one hour?
41 "Keep watching and praying that you may not enter into temptation; the spirit is willing, but the flesh is weak."
42 He went away again a second time and prayed, saying, "My Father, if this cannot pass away unless I drink it, Your will be done."
43 Again He came and found them sleeping, for their eyes were heavy.
44 And He left them again, and went away and prayed a third time, saying the same thing once more.
45 Then He came to the disciples and said to them, "Are you still sleeping and resting? Behold, the hour is at hand and the Son of Man is being betrayed into the hands of sinners.
46 "Get up, let us be going; behold, the one who betrays Me is at hand!"
This clearly shows that Jesus had the choice of not following God's will. He was almost sinning there. I've passed through moments when I knew that I shouldn't sin and I had to keep control. It is NOT easy and in this situation it was DEFINETLY way harder. This means that Jesus also had the choice of not believing He would be raised from the dead, which makes it a really great sacrifice. The possibility of His loss wasn't something easy to stand.