To be precise, here is the relevant text from 17 USC 203: (a) Conditions for Termination. — In the case of any work other than a work made for hire, the exclusive or nonexclusive grant of a transfer or license of copyright or of any right under a copyright, executed by the author on or after January 1, 1978, otherwise than by will, is subject to termination under the following conditions:
(1) In the case of a grant executed by one author, termination of the grant may be effected by that author or, if the author is dead, by the person or persons who, under clause (2) of this subsection, own and are entitled to exercise a total of more than one-half of that author's termination interest. In the case of a grant executed by two or more authors of a joint work, termination of the grant may be effected by a majority of the authors who executed it; if any of such authors is dead, the termination interest of any such author may be exercised as a unit by the person or persons who, under clause (2) of this subsection, own and are entitled to exercise a total of more than one-half of that author's interest. ... (4) The termination shall be effected by serving an advance notice in writing, signed by the number and proportion of owners of termination interests required under clauses (1) and (2) of this subsection, or by their duly authorized agents, upon the grantee or the grantee's successor in title. (A) The notice shall state the effective date of the termination, which shall fall within the five-year period specified by clause (3) of this subsection, and the notice shall be served not less than two or more than ten years before that date. A copy of the notice shall be recorded in the Copyright Office before the effective date of termination, as a condition to its taking effect. ... (b) ... (1) A derivative work prepared under authority of the grant before its termination may continue to be utilized under the terms of the grant after its termination, but this privilege does not extend to the preparation after the termination of other derivative works based upon the copyrighted work covered by the terminated grant. So: 1) a copyright transfer (or reaffirmation of previous copyright transfer) contained in the author's will is not terminable by the author's personal heirs, so you can certainly block their ability to terminate if you so choose; 2) the "50% rule" applies to _authorship_, which connotes (per Aalmuhammed v. Lee) a degree of creative control so high that, e. g., there is no candidate for "authorship" of the Linux kernel other than Linus Torvalds; 3) a later work that incorporates fragments of protected expression from the original is only encumbered if its use of that expression rises to the level of a "derivative work" requiring explicit grant of license, which would imply that the amount of _copyrightable_ expression copied is more than "de minimis" relative to the size and scope of the final work. Given the proportion of a typical piece of software that is uncopyrightable on grounds of "scenes a faire", "ideas and methods of operation", and so forth, it is quite unlikely that a copyright infringement claim could succeed thirty-five years after the creation of the original unless substantial, identifiable chunks have been literally copied. And if the maintainers can't reimplement those chunks without plagiarism in two years' time, they have problems much larger than those posed by 17 USC 203. Cheers, - Michael
