[RPG] Is Bahamut the same deity as Paladine

There are many factors depending on the setting. Although there is lore common to many D&D settings, even that lore is subject to change—possibly radically so—in any given campaign or setting. When it comes to settings DMs make themselves, that is doubly true.

In this case, there may be precedents set by other campaigns and other settings, but there is no universal lore on how to kill a god. Certainly, there is none that automatically and officially applies to your home setting.

So the question becomes: what is the lore in your setting for how to kill a god?

You have some good ideas already that I'd encourage you to follow up. They accord with some ideas that others have had about how deicide can be accomplished, so you can at least take comfort in like minds having walked similar paths before.

• Making a god mortal first is a common idea. This is how gods in the Forgotten Realms have been killed before.
• Similarly, a dead god is rarely completely dead, just mostly dead. There is Planescape canon of dead gods floating through the astral, just waiting to have devotees perform some great cosmic rite to awaken them.

Just remember that plausibility doesn't enter into it. How a god can be killed in your setting is simply a cosmic truth—it is what it is—with no need to justify itself to the sense of plausibility of mere mortals. Make it interesting and revelatory to your players, and that should be enough.

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).