While Sharepoint might some day die, it will only be replaced by another piece of software that gets launched for nobody to ever use.
I have worked at an org that did the same. We already had Confluence. Somebody decided we needed Sharepoint. We licensed and installed it. Six months later we migrated the handful of documents and files and decommissioned it.
probably so. every corp I've worked for that had Sharepoint used it religiously. that is a whopping 3 different companies, but > 1 anecdotal experience. to be fair though, 2 of the 3 companies used it because the same person was at both companies and was responsible for using it at both companies during their tenure.