Probably like they did during the Great Wheel Era, those are just divine realms that are located on one of the outer planes. With a pre-3e sourcebook we could even look up where exactly these places used to be locatedI didn't vote for FRs world tree, but I will say its had alot of cool stuff, it had a ton of potential, but they did nothing with it. I mean all those FR books in 3.5e and not one Forgotten Realms Manual of the Planes style book to flesh them out was a wasted opportunity.
Btw FRs World Tree isn't completely dead in 5e, the plane of Zigguraxus is mentioned in one of the last Brimstone Angels novels that Gilgeam and Enlil were completing to restore, which was intended as one of the World Tree Planes, but kind dead when the Untheric Pantheon fell apart after Gilgeam's death.
How the restoration of the planes of Zigguraxus and presumedly Heiropolis (the Mulhorandi Gods), not to mention the continued existance of the Towers of Night Plane from FR's version of the World Axis cosmology fits in with 5e Cosmology is an important question.
It suggests that the great wheel outer planes are not the only outer planes in 5e.
I'm shocked the world Axis is beating Planescape.
Only due to the two great wheels being counted separetely which I don't really see a point to. IMHO the differences are too minor, they're the same cosmology