The Silmarillion Survivor

[Formendacil]

Originally Posted by Anguirel

The Kingship is also a vital issue. Think what the scheming uncle may do to his nephews once the throne is his! I implore Feanorians back the guile, craft and staying power of Curufin. Remember, he has an heir; Maedhros doesn't...

If by "heir" you mean "son or daughter" then you or correct. If you mean "legitimate successor", then Maedhros has no lack, and with these being Elves, there is no need for lifespan to be a concern. They are, in order* (counting only Elves or those who choose Elvenkind...):

Maglor, Celegorm, Curufin, Celebrimbor, Caranthir, Amrod, Amras, Fingolfin, Fingon, Turgon, Idril, Earendil, Elrond, Elladan/Elrohir, Aredhel, Maeglin, Finarfin, Finrod, Aegnor, Angrod, Orodreth, Gil-Galad, Finduilas, Galadriel, Celebrian.

As you can see, no lack of heirs.

*According to ONE possible geneaology