Your dad can DIVORCE on whatever grounds the laws of his land allows him. JW permission to REMARRY, however---to pursue another mate---is where his hands are tied, unless or until adultery is committed by his ex-spouse. If there was no adultery during the marriage, then to remain in good standing AND be available to remarry, your dad would have to wait for her to commit 'adultery' after the marriage.
He will be forced to wait until it becomes publicly known that his now ex-wife has had sex with a new man. If she starts living with another man, or stays overnight unchaperoned, or marries another man, then sexual relationship is implied, and your father is free to pursue a new relationship at that point-----and no sooner. That lacivious action by the ex-wife, POST-divorce, establishes her as the adulterousbad-guy and leaves your dad smelling like a rose and swarming with single-sisters' sympathies.
[It wouldn't matter at this point what kind of husband he had been during the marriage and what kind of hell he might have put his ex-wife through that prompted her to leave the failing marriage in the first place. All that matters is that he did not break this one cardinal rule--she did.]
--That was not a statement about your dad, BTW. I don't know him. It was about the unjust and small-minded stipulations the JW's put on happiness.