How can we show whether the Hebrews knew of survival after death?

Many today deny that they knew, appeal to a supposed unitary concept of man, i.e., a body with breath in it. But the determined belief in necromancy we find in the OT shows they did know of a survival (Lev 19:31 and 20:6; Dt 8:11), even if they did not knowhow to reconcile that with a possible unitary concept of man.