Overnight travelers can use Night Tube services on the Piccadilly line on weekends

https://charliellav811.tearosediner.net/how-do-i-get-to-heathrow-terminal-4-step-by-using-step-routes-and-tips

Overnight travelers can use Night Tube services on the Piccadilly line on weekends, or consider night buses that connect to Heathrow’s central bus station.