> However, nonexclusive licenses are revocable (meaning the copyright owner can revoke the license at any time) in the absence of consideration. 
> https://www.dmlp.org/legal-guide/creating-written-contract-transfer-or-license-rights-under-copyright

>  [...] The most plausible assumption is that a developer who releases 
>  code under the GPL may terminate GPL rights, probably at will.
>  --David McGowan, Professor of Law, University of Minnesota Law School:

> p278 "Notice that in a copyright dispute over a bare license, the
> plaintiff will almost certainly be the copyright owner. If a licensee
> were foolish enough to sue to enforce the terms and conditions of the
> license, the licensor can simply revoke the bare license, thus ending
> the dispute. Remeber that a bare license in the absence of an interest
> is revocable."
> --Lawrence Rosen
> https://www.amazon.com/Open-Source-Licensing-Software-Intellectual/dp/013148787