400 years of slavery will mold the mind of any people and it is hard to claim, for instance, that a group living in the United States for such a long period will not acquire the basic psychology of American people, neither it is reasonable to assume that Israel forgot what they incorporated as part of a daily routine.
However, we know from the Exodus record, etc., that a deliberate effort was made to stamp out the residue of Egyptian thought and practice and set the minds of the people in completely different direction--even to the extent of letting almost all of the Egyptian escapees die off before the remaining population entered Canaan. Much of Deuteronomy is devoted to an effort to inoculate the people against the customs and beliefs of the Canaanites.
For example, the concept of a deferred resurrection of the physical body after a long period in the grave (e.g., Job 19:25-27, and Eccl. 11:8) could scarcely have been confused with an immediate transport of the soul to another form of existence.