Giacomo Meyerbeer
Scribe died in 1861.  Meyerbeer worked very hard to try to finish his last opera,  L’Africaine.  Napoleon III said he wanted the opera to be ready by the winter of 1862-63, but it was not ready until 1864.  The work was being rehearsed for its first performance when Meyerbeer suddenly died, without having had the chance to revise it, the way he revised most of his other pieces.