NOTE: Under the Doctrine of Esstopel, if you proceed on this basis and two years pass without their heirs bringing an action of some sort, then under thisMakes me wonder if something should be done to address the issue of dead copyright holders. Not sure what but maybe there should be a clause in GPL3 addressing that?
Their heirs would have two years to bring a cause of action if they object. Proper notice could be served by posting a notice on the internet at kernel.org
that their code is being redistributed under GPL3. I note that the general notice in the code states "GPL2 or any later version of the license". Given this
language, it is highly likely the remaining code can proceed under a new license without incident since it can be assumed they already agreed by
having this general notice posted at kernel.org for many years. I think the point is moot. Legally, there is exposure if their successors or owners
of their estates bring action. Those outside the US would of course be subject to the laws of their jurisdiction. An attorney at FSF needs to review their
code and render an opinion, but I think it will not be a problem.
Jeff