It is my understanding it is against Miss. Law for the loser of a primary to run in the General Election as a Write in candidate.
My understanding is that the write in line is reserved for a circumstance when any one of the named candidates is unavailable for non-political reasons. If the GOP nominee dies, then a GOP candidate's name can be written in that line, etc.
So, a primary loser could well become the party's preferred candidate.
But, if Childers becomes unavailable for non political reasons, I don't think a vote for a GOP primary loser is counted, if written in.