Gnome Memorial Mountain is here to stay forever.
XP bonus ends at 1 AM on April 1st (likely PST but not sure)
14th through 20th Anniversary events runs until May 10th
5th through 13th Anniversary events start April 12th and run to May 10th
Sources: /calen in game
https://events.eqresource.com/index.php ... &year=2019
http://everquest.fanra.info/wiki/Annive ... .282019.29