The Others In Two Timelines

In Poul Anderson's The Game Of Empire, Axor's quest for the Universal Incarnation was initially inspired by Foredweller remains/relics/remnants on his home planet, Woden. We know from Anderson's The Day Of Their Return that remnant walls and indeed entire structures also exist on the planet Aeneas. Diana has heard that the Builders were "the Chereionites" and an Aenean spaceman referred to them as the Old Shen. Other names are Ancients, Elders and Others. That the Chereionites were the Ancients is indeed what Aycharaych, a Chereionite, told Erannath, an Ythrian, on Aeneas in The Day Of Their Return but who knows?

What does Axor expect? An eventual multi-species religion acknowledging two Incarnations, Terrestrial and Chereionite? (Or whichever species the Forerunners turn out to be?)

It turns out that "They" are not about to "Return." That was a deception fostered by Aycharaych. However, Marc Vitrac and his companions in SM Stirling's The Sky People are in a more perilous predicament because they have learned not only that the inhabitants of Venus are human but also that the language spoken there is Indo-European! It follows that the superior technology that terraformed Venus and Mars and seeded those planets with Terrestrial organisms was still active comparatively recently and therefore might still be around - unlike Anderson's long-gone Ancients.