Question:

Did those baptized by John the baptist have to be "re-baptized" after Jesus was crucified?

Answer:

John's baptism was different from Jesus' baptism. See "How was John's baptism different from Jesus' baptism?" for details. Though at least some of the apostles appear to have been baptized by John, they were baptized into Jesus' baptism. "After these things Jesus and His disciples came into the land of Judea, and there He remained with them and baptized. ... And they came to John and said to him, "Rabbi, He who was with you beyond the Jordan, to whom you have testified -- behold, He is baptizing, and all are coming to Him!" ... Therefore, when the Lord knew that the Pharisees had heard that Jesus made and baptized more disciples than John (though Jesus Himself did not baptize, but His disciples), He left Judea and departed again to Galilee" (John 3:22,26; 4:1-3). It is a mistake to assume that Jesus' baptism only began after his death.

When Paul ran across men in Ephesus who were baptized, he discovered they did not know about the Holy Spirit. Such could not be possible for those properly baptized since baptism is done in the name of the Spirit (Matthew 28:19) and a consequence of proper baptism is receiving the gift of the Spirit (Acts 2:38). The result was that these men who had been baptized into John's baptism were baptized again into the name of Jesus (Acts 19:1-7).

So yes, people baptized by John were baptized again in Jesus, but not all were baptized into Jesus after his death. Some were baptized into Jesus before his death.