Any JW has one of the main deep-down doctrines that holds them 'captive'.
That is of 'universal sovereignty'. That is only one of the key cornerstone doctrines which they are captive to and abide by. Any JW will argue 'adamantly' to the fact that there is only life here on one planet, ours Earth.
Should life be proven anywhere else but Earth, one of their cornerstone doctrines comes tumbling down. In many JW's mind their bible would be ruined. On a personal matter I would be just fine if life were proven elsewhere.
Some would argue that ''there is no scripture saying life does NOT exist elsewhere'' in the universe. But yeah to a great many JW's their belief system takes a major, major devastating hit. In other words 'their bible'' would be destroyed.