There were many possibilities and opportunities for Jesus to lay down his life for us. Scripture tells us of a few:
John 7:1
After this Jesus went about in Galilee; he would not go about in Judea, because the Jews sought to kill him.
Luke 20:19-20
The scribes and the chief priests tried to lay hands on him at that very hour, but they feared the people; for they perceived that he had told this parable against them. So they watched him, and sent spies, who pretended to be sincere, that they might take hold of what he said, so as to deliver him up to the authority and jurisdiction of the governor.
John 7:30-33
So they sought to arrest him; but no one laid hands on him, because his hour had not yet come. Yet many of the people believed in him; they said, "When the Christ appears, will he do more signs than this man has done?" The Pharisees heard the crowd thus muttering about him, and the chief priests and Pharisees sent officers to arrest him. Jesus then said, "I shall be with you a little longer, and then I go to him who sent me;
There are other verses as well but these are enough to demonstrate that Judas was not the only possibility. God's plan for salvation permitted Judas to be the instrument of betrayal. There is a lesson in this for us. Judas was a disciple. Likewise, we are disciples. Judas was blessed with grace and he even healed the sick and cast out demons with the rest of the apostles.
Likewise, we are blessed with grace. Like Judas, we can betray our Savior. All men are free to accept or reject God's grace. Grace enables but it does not force us. We must always put the Lord ahead of all things in our lives and never betray the Lord or the salvation that God has given us.