Hey,
Unfortunately with Witch Queen's release, Season of the Lost will be vaulted along side its story missions, while I understand this can be frustrating this is how the narrative is set out by Bungie.
So you will only be able to play the mission during Season of the Lost.
English
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Imagine buying a game, playing thru it just to be stopped before last mission with a message saying “Last mission only available 13 of may between 3-5 am” If you can’t be online, unlucky, go eff yourself, thanks for your money!