Here I offer relevant commentary, epitomized from H24H 15§§33–34:
{15§33} The three cult heroes, as mentioned here by Pausanias, all qualify as theoi, ‘gods’, in the context of the hero cults that had been established in their honor. Pausanias says about Amphiaraos that the worshippers of this cult hero at Oropos considered him to be a theos, ‘god’, and all Hellenes eventually accepted such a status for this cult hero; in the same context, Pausanias then goes on to say that the same status of theos, ‘god’, was eventually accepted by all Hellenes in the cases of the cult hero Trophōnios as worshipped at Lebadeia in Boeotia and the cult hero Protesilaos as worshipped in the Chersonesus. Such a formulation is typical of the era of Pausanias, the second century CE, by which time the distinctly localized aura of hero cults was receding and giving way to the far brighter Panhellenic publicity that was being generated by the most famous cult heroes of the time, such as the triad of Amphiaraos, Trophōnios, and Protesilaos. That said, I should emphasize that this triad of cult heroes was already famous in the era of Herodotus, who lived over 600 years earlier than Pausanias. In the case of Protesilaos, Herodotus gives him a most significant role as a cult hero who guards against injustice, as we see especially at 9.120.1–2; in the case of Amphiaraos and Trophōnios, Herodotus at 1.46.2 mentions both of them together in the context of narrating oracular consultations made by Croesus, king of the Lydians, at the sites where these two cult heroes were worshipped. Still, my point remains that the mysteries concerning the death and the resurrection of all three of these cult heroes were becoming ever less mysterious in the era of Pausanias. Correspondingly, the eventual status of such heroes as theoi, ‘gods’, became ever more obvious to all.
{15§34} The death of Amphiaraos is a most telling example. In the version of the relevant myth as retold by Pausanias at 1.34.2, Amphiaraos is riding back home on his war chariot after the defeat of the Seven against Thebes, when suddenly the earth opens up underneath and swallows him—speeding chariot and horses and all; and, at the spot where this engulfment happened, there is a hieron, ‘sacred space’, where worshippers of the hero come to consult him, though Pausanias observes that there was some disagreement about matching the place of the ritual consultations with the actual place of the engulfment. In any case, the engulfment of Amphiaraos by the earth is a sign of his death and of his subsequent return from death as a cult hero. In Odyssey 15, lines 247 and 253, the death of Amphiaraos after the expedition against Thebes is made explicit, though it is only implicit in the references to the engulfment of this same hero as narrated in the songs of Pindar, at Olympian 6.14, Nemean 9.24–27, 10.8–9. The poetic reticence we see in Pindar’s songs about mentioning the actual death of Amphiaraos at the moment of his engulfment by the earth is a sign, I argue, of a keen awareness about the subsequent resurrection of the hero. Further comments at BA 154, 204 = 9§5,10§41n3.