ftD, willful rejection of baptism is probably a sign that the person has not truly become a believer in the Lord.
That is different then saying that the person is not saved because he is not baptized.
There is a school of theology that believes that water Baptism is not for the church age.
It could be ignorance on someone's part as well as rejection of water baptism as being legimate.
Faith in the person and work of Christ is what saves, and Baptism is a sign of that salvation.
Rejecting the 'sign'cannot effect the salvation.