1 Cor, 7:12 But to the others I say, yes, I, not the Lord: If any brother has an unbelieving wife and she is agreeable to staying with him, let him not leave her; 13 and if a woman has an unbelieving husband and he is agreeable to staying with her, let her not leave her husband. 14 For the unbelieving husband is sanctifiedin relation to his wife, andthe unbelieving wife is sanctified in relation to the brother; otherwise, your children would be unclean, but now they are holy So having an unbeleiving mate allows that one a free ticket to the new world.
The WTS specifically says this is not the proper application...but it only makes minor children holy, so at Armageddon the children will survive if only one parent is a jw. It's in a QFR somewhere, maybe even here on JWN.