I was reading about Bahamut in the forgotten realms wiki, and in it it states that he died. However it also states that he is a god. So I'm curious, is Bahamut still alive or did he simply die on the mortal plane?
Bahamut is alive and well
On page 86 of the 5e monster manual, Bahamut is spoken of in the present tense.
Tiamat's most hated enemy is Bahamut the Platinum Dragon, with whom she shares control of the faith of dragonkind.
On page 298 of the Players Handbook, under "Nonhuman Deities" the first entry is:
Bahamut, dragon god of good (Align LG, Domains Life/War, Symbol Dragon's head in profile)
PHB p.293 indicates that the table on p. 298. is shared by both FR & Greyhawk, so it should be valid for FR. (Credit to @CTWind)
The reports of his demise are premature, if you accept 5e D&D as a valid state of being.
(From comments under the question)
you're asking if Bahamut is alive in 1489 DR? Is that the question? – @SevenSidedDie
Yes Sevensideddie, that is correct. – @Bigbo Biggins
The campaign date of the Forgotten Realms 1491 DR coincides with the real-world year of 2015 (Princes of the Apocalypse campaign). Per your comment, in terms of DR 1492 ... he's not dead (yet).