prologos,
The February 15, 2008 Watchtower says that Jesus' promise means that some of the Anointed will remain on earth until the BEGINNING of the Tribulation (however, Watchtower articles this year have updated this and said that some of the Anointed must remain on earth until the judging of the Sheep and Goats right before Armageddon):
Watchtower, 2/15/2008:
Christ’s faithful anointed brothers, the modern-day John class, have recognized this sign as if it were a flash of lightning and have understood its true meaning. As a class, these anointed ones make up the modern-day “generation” of contemporaries that will not pass away “until all these things occur.”* This suggests that some who are Christ’s anointed brothers will still be alive on earth when the foretold great tribulation begins.