system
Given the following post, respond as if you're commenting on Reddit:
human
(Warhammer 40k) Have any of the races around 'today' left the Galaxy?

Barring Nids obviously as they come from outside already.

During the Macharian Crusade the Imperium failed to leave the Galaxy and would have trouble navigating anyway as the astronomican doesnt reach that far out. 

However races such as Eldar and Necrons surely have the technology to leave the Galaxy? Are there any reported instances of such?
gpt
The Silent King Szarekh left the Galaxy after he destroyed the Old Ones, enslaved the C'tan, and destroyed the command protocols of the entire Necron race while sending them to sleep. He supposedly left to find peace and "penance" for his sins. He returned to the Milky Way about 60 million years later to warn the Necrons about the Tyranid threat he encountered in the intergalactic void.