Welcome to the forum Amberlou,
Unless your BF realizes for himself that the JW religion is not "the truth" and is a cult, there is always a high risk that he will return to it, even if he now denies that.
The lack of relationship with his family due to him not being a JW will be his family's decision. If his family is willing to break ties and turn their backs on him only because he decided he no longer wishes to remain a JW, then they really don't deserve him or you.
Will you ultimately accept and respect your BF if he changes who he is so as to satisfy the demands of his relatives? Even if he were to cave into their demands, do you believe they will then accept his relationship with you?
Giving into demands of relatives is a slippery slope. If he allows them to control him because he fears their rejection, reinstatement will not be enough but they will continue to place further demands on him to continue their approval.