If it was indeed possible to revoke a FOSS license at will nobody in their right mind would dare to rely on open source for their business. So while some licenses, such as the Apache License version 2.0, explicitly state that the licenses granted are perpetual I'd say it's reasonably safe to assume that this applies even where not stated for any situation where the author simply changes their mind about the license.
What you can do if you change your mind about the licensing of your work is to release any future updates under a different (proprietary or FOSS) license. However, already released versions can still be used in any waý the license under which they were released permits.