In the New Testament death for a believer is spoken of as “sleep” (1 Cor 15:6) but at this point in time there was not yet a resurrection of the Messiah, nor a New Testament and the disciples did not pick up on the meaning of what Jesus was saying.

1 Corinthians 15:6  After that, he appeared to more than five hundred of the brothers at the same time, most of whom are still living, though some have fallen asleep.