This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / The Edge Chronicles
Keris being united with her grandmother at the end of The Slaughterer's Quest.
Cloud Wolf being absorbed into the Mother Storm while Twig tries desperately to keep him alive.
That poor banderbear in Beyond the Deepwoods. Twig's finally made a friend who doesn't hate or bully him, only to be devoured by those damn wig-wigs.
Twig wiped his eyes and looked down. The wig-wigs had gone. And of the banderbear, there wasn't a trace to be seen, not a bone, not a tooth or claw, not a single scrap of mossy fur. From far away there came the forlorn yodelling call of a distant banderbear. Time after time its heartrending cry echoed through the trees. Twig held the tooth around his neck tightly in his hand. He sniffed. "It can't answer you now," he whispered tearfully. "Or ever again."
Twig accidentally finding his way back home via a woodtroll path in Midnight over Sanctaphrax, only to walk in on his father's, Tuntum's, funeral. Made even more tear-worthy when you realize that he's now lost both fathers in one fell swoop.
Twig losing his entire hand-picked crew on his attempt to return to Riverrise for the second time. And then, when the caterbird finally flies him all the way there at the end of his natural life.. Maugin is shot seconds before he lands and Goom and Woodfish have both wandered off years previously.