After i died, i saw a dog tag that i didn't pick up but i thought dog tags disappear after you died. So how long do they last? Or they never disappear until you pick em up?

In the demo it did disappear after you died, must be a bug or something

i think its only for a few min. or maybe until u die again

In the demo atleast for pc the dogtags remained for a set period of time no matter whether you died or not. Not sure the exact time but they do disappear.