What do I do if I lost a piece that broke off a Sefer cover (may have been thrown out by now) from a Lamed Tes Melachos Sefer?
The cover of a sefer has to go into geneiza. However now that it is lost, there isn’t much that you can do about it. The idea for putting things in to geneiza are because we are not allowed to throw them out in a disrespectful manner. You can comfort yourself with the thought that right now that it is lost, you are not doing anything disrespectful to the cover, you just can’t put it into shaimos.