system
Given the following post, respond as if you're commenting on Reddit:
human
[40k] Abaddon and a small company of his chosen get lost in a warp storm and end up on present-day Earth. What happens next?

Obviously he can't rage at the Emperor and the Imperium cause they aren't a thing yet. Well the Emps is here but no one knows where. What does Abaddon do?
gpt
The Emperor most definitely exists as a person at that point, he's just either working behind the scenes or he is living as a 'normal' human would live, with a family, job, etc and occasionally faking his death.  

I would bet he would sense something about Abaddon, a familiarity but also his corruption.  Even before he was Emperor, the man who would become Emperor was a force of immense proportions.  His psychic powers and physical abilities were immense but purposefully shielded from the humans of Earth who were not ready to realize him in his glory.  

Abaddon has two options, he can either make a big show of himself and attempt to draw out the Emperor, such as attacking cities or killing innocents or he could attempt to find the Emperor through subterfuge.  Either way the Emperor probably wouldn't like being called out/searched for.  Either way Abaddon would be picking a losing fight.