I'm looking for songs with lyrics about the future, but that future already passed. For example, the Sanctuary song The Third War with lyrics asking if the world will end in the future year of....1999. Or their song Future Tense asking what the nineties will hold. Any genre is fine.

Accept - Metal Heart, one of the best heavy metal songs ever recorded. Begins with "It is 1999..."

Helloween - Twilight of the Gods, "Insania 2014..."

Dream Theater - New Millenium I guess?

Some bands did songs on 2012, when the Mayans supposedly said the world would end. I remember Therion but there must be more.

In 3 years you can use Satan's Twenty Twenty Five!

Running Wild - Genesis (The Making and Fall of Man): a 15 minute power metal epic that has the lyrics "In the 7th month of the year 1999 an ancient god of wrath will return bringing fire, water, death and destruction".

So... would Sarcofago's "you will be burned and died" technically count as future past tense ?

Beherit's Dawn of Satan's Millenium. I'm not sure what the lyrics actually say, but but since the song is from '91, and its Beherit, we can assume the lyrics are wrong.

Megadeth - Set The World Afire (1988)

"Distorted figures walk the street, it’s 1999
Weeds once underneath your feet have grown into vines
Bodies melted like a candle, a land without a face
No time to change your fate, no time left, it’s too late"

God Dethroned’s “2014” fits.

“In 2014 they take the world by storm.
We don't know who they are, but they'll come that's for sure.”

And then lines about the apocalypse and Nostradamus prophecies not going beyond that year.

On a similar note to Sanctuary, there's Metal Church's Beyond the Black...

"The war is over
The crypt we now taste
In the late 1900's, there is no human race
We split the planet with atomic birth
Man has died
We seal the urn."

Any genre is fine? Saga - The Nineties (1989).

Not metal but Bad Religion's Ten in 2010

Borknagar - Future Reminiscence comes to mind. Iron Maiden - Days of Future Past is at least in title/chorus, though it seems to be more about everlasting punishment in hell.