It had a good run
Square Enix has confirmed plans to cease support for the game's console versions on March 31 at 6am PST, after which time the servers will no longer function on those platforms.
For now, the faithful have the option to continue their adventures in Vana'diel by switching over to the Windows edition. However, it's unclear how much longer the lights will stay on. While Square Enix is still rolling out minor updates and is even working on a mobile version with Korean studio Nexon (Maple Story, Dragon Nest), the party has to end sometime, right?
Unless it doesn't. Who knows? Maybe Final Fantasy XI will outlive us all.
Final Fantasy XI [Square Enix]