no, someone may NOT be rebaptized “just in case”. If the validity of the first baptism cannot be demonstrated, or its occurence proven or attested, the individual may be conditionally baptized. That is not the same thing.
The validity of the baptism in this case depends on the proper matter, form and intention. For most denominations this is a matter easily determined based on their stated practice and belief. Where there is question the bishop investigates and rules. Where they are demonstrably lacking, the Church has declared their baptisms invalid, Mormons and Witnesses among these, because the intent of baptism is to bring one into the Christian communion, and neither of these sects is Christian. anyone may baptize, even a non-Christian, if the three elements are present.
If someone is dying, call 911 and tend to their needs and pray while you wait for the paramedics.