I think copyright is inherited by the heirs (in most cases relatives of the deceased) and carries on quite a long time after death. So the relatives may actually sue you, and any discussion WRT relicensing would have to be addressed to them.
I actually consider putting something into my will that states that all my open-source contributions are relicensed to "public domain" (CC0 [1]) once I die.
Its also possible to transfer your copyrights before your death. For example to the FSF or to Software Freedom Conservancy. I hear there are tax implications for copyright bequeathment, which is why transferring copyrights is preferred.
I actually consider putting something into my will that states that all my open-source contributions are relicensed to "public domain" (CC0 [1]) once I die.
[1] https://creativecommons.org/share-your-work/public-domain/cc...