I've been interested in the Romans a lot lately, due to the big impact christianity had on the later Romans a bit of cross reading on early Christianity also came into this. From here the obvious old idea struck me- what if Jesus died when he was still a child, before he had time to go off and found his religion?
The big idea rattling around in my head from this is- John the Baptist. He becomes the head of some sort of Baptist Jewish cult which could possibly spread to the gentiles and become a sort of christianity lite?
Nonetheless...considering how bizzare it was some little cult took over the Roman empire IOTL its unlikely anything else whether it be Baptism, Mithrasism, etc... could replace it in quite the same way. The implications are of course very interesting...