That would require getting confirmation from all contributors, including those you can't find and from the executors of those who no longer exist.
They aren't relevant if you are worried about a "kill switch revolt", since those you can't find probably won't even know what is going on that they may want to revolt again, and those who are dead aren't likely to have their executors revolt on their behalf.
Though I really question whether a kill switch revolt would be possible at all under GPLv2. Once you've given permission for a certain blob of code to be used and copied freely into other GPLv2 code I don't see how you can revoke that permission. Furthermore, if you were developing a GPLv2 application and found some code covered under GPLv2 on the net that you want to incorporate into it, how the heck are you supposed to know if one of its contributors has later revoked permission?
I just don't see what legal basis there could be for this - you hold the copyright, but by contributing and allowing its inclusion to a GPLv2 work you've granted a license to use that code under GPLv2. You still hold the copyright, and could turn around and sell the rights to use that code for $1 million to Microsoft or whoever for some closed source product, which is a second license. You can't later revoke the GPLv2 license any more than you could revoke the license you granted to Microsoft (even if you paid them back the $1 million)