Jason of the Argonauts survived a voyage to the end of the world; some time long after his travels are done, after the whole tragic mess with Medea, he dies when a piece of the Argo's prow breaks off and hits him on the head. Euripides was the first writer to mention how he died, making this Older Than Feudalism. He died alone, miserable, and unloved, killed by the prophetic prow provided by the patron goddess he betrayed.
Theseus, king of Athens, slayer of the Minotaur and victor over the Amazons, might be the most famous hero after Herakles. His demise? Lycomedes, the king of Scyros, treacherously pushed him off a cliff and never suffered consequences for it.