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

https://www.scribd.com/document/1074894734/Heathrow-Drop-Off-Charges-and-Pick-Up-Locations-Avoid-Fines-and-Hassles-212266

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.