While broken, I suppose this is what would happen: 1. Person A writes project X under GPL 2. Person B extends project X under GPL 3. Person A removes all tra

While broken, I suppose this is what would happen: 1. Person A writes project X under GPL 2. Person B extends project X under GPL 3. Person A removes all traces of contributions from project X and releases under non-GPL 4. Person B rightfully continues to use project X under GPL, possibly even hosting a fork and continuing collaboration. (I'm not sure if step 3 is feasible - while person A is free to use their own copyrighted work however they please, it might not be possibly to legally erase all trace of foreign contributions.) --- What normally should happen is that Person A needs to contact all contributors, and have them agree to the relicense their contributions. If all authors agree, then there is no issue. However, step 4 still applies - everyone receiving the code under GPL is free to keep using (and distributing) it under GPL. Only contributions done to the relicensed work will be uniquely protected by the new license.