In the 1937 Silmarillion, which contained the last full version of the End of the First Age that Tolkien ever wrote, there are two conflicting accounts of the fate of Maglor. The first one, from paragraph 25, is the best known, and was taken up in the published Silmarillion:
...thereafter he wandered ever upon the shores singing in pain and regret beside the waves. For Maglor was the mightiest of the singers of old, but he came never back among the people of the Elves.
The second one however, from paragraph 28, has an entirely different fate:
Yet not all the Eldalie were willing to forsake the Hither Lands where they had long suffered and long dwelt; and some lingered many an age in the West and North, and especially in the western isles and in the Land of Leithien. And among these were Maglor, as hath been told; and with him for a while was Elrond Halfelven, who chose, as was granted to him, to be among the Elf-kindred...
This was not amended (or at least not recorded as having been amended) in the post-LotR revisions of this part of the Silmarillion, and so must have most likely been editorially changed (to "
Among those were Círdan the Shipwright, and Celeborn of Doriath, with Galadriel his wife, who alone remained of those who led the Noldor to exile in Beleriand. In Middle-earth dwelt also Gil-galad the High King, and with him was Elrond...") in Chapter 24 by Christopher Tolkien.
It's difficult to know how to interpret this. On the one hand "among these were Maglor" does not directly contradict the first paragraph (he may have just been wandering alone in the same regions). On the other hand "with him for a while was Elrond Halfelven" clearly shows that Maglor was not alone. But yet again, Elrond as "Halfelven" could be argued to not belong to the "people of the Elves". The only thing that seems certain is that Tolkien had Maglor living with Elrond as a reference to Maglor's earlier succouring of the sons of Earendil, but what his ultimate intention was seems as though it must remain unknown.
A final point is the reference to "
that lament which is named Noldolante, the Fall of the Noldor, that Maglor made ere he was lost" in Of the Flight of the Noldor. Again, this is open to individual interpretation - did he make it during his wanderings? Did he make it during his time with Elrond? Did he make it earlier in the First Age?
Ultimately the whole matter is best summarized by Tolkien's words elsewhere: "
of this two things are said, though which is true only those Wise could say who now are gone".