I too understood that some of the 144,000 would still be alive at Armageddon. Supported by 1 Cor 15 v 50-52.
''We shall not all fall asleep in death, but we shall be changed, in a moment, in the twinkling of an eye......''
Another Scripture (which I cannot recall) suggests that the Great Tribulation will be cut short when God's enemies touch 'the Apple of His Eye' (When the remaining 144,000 are 'attacked', God will bring the 'End').