If he didn’t exist in the first place, the worship Cimmerians give to him might cause something from the Outer Dark to assume Crom’s mantle.
It’s like the one of the early bosses in the Age of Conan: Kothar-Wa, the Bat God. The local Picts worshipped the Bat God - an entity that didn’t exist.
The AoC main character was a person possessed by a demonic spirit (implied to be an Acheronian soul) before being exorcized by Kalanthes. The disembodied demon fled into the jungles of Tortage and found the Acheronian ruins, inhabited by aforementioned Picts. So it hijacked their religious beliefs, assumed a corporeal form and became the real, existing Bat God.
Your characted is later called out for it by some locals and sent to “rectify the problem” and kill the monster.