In the future most FOSS projects will be abandoned, and when they run out of copyright term, the closed source companies will start using them with modification without releasing the source.Even Linux only belongs to Linus, 50-70 years after Linus’ death. Will the software of today become obsolete, 50-70 years after its author’s death? (e.g. 48 core limit on current OSes) I do not know. But the oldest algorithm, the Euclidean algorithm is 2300 years old. And it is still widely in use today as a key element of the RSA algorithm. So we ought to not expect all software of today to become obsolete a century from now. Some of them will remain useful and will be used as closed source in future.
My point is that if you are after FOSS because of some misguided sense of altruism, your sacrificial offering will put to use by those who accept sacrifices for their own benefit.
We see how Sun software became closed source after Oracle bought Sun. That is a glimpse of what is to come.