Well my dad is SB (Southern Baptist) but since my mom remarried a JW I grew up very very JW. I kept my JW ways when I visited my dad due to thinking I was being lured by Satan to betray Jehovah by participating willingly (versus bystander) in my Dad's 'pagan' ways.
But this all said the Pew Report states JW born/raised retention rates to be only 37% (yep 63% leave the JWs).
Yes a marriage can be 'reasonably happy' in 'mixed' marriages so long as respect and balance is sought over debating who is right or wrong.
Focus on what is agreed and understand that each parent has the right to share POV with the child on items where disagreement occurs.
For instance as a JW I taught my children that Xmas has pagan origins, hubby on the other hand points out that you can't swing a dead cat without hitting 9 things out of 10 that can be linked to something pagan. My kids have been taught both trinity and arianism, immortal soul and asleep in death. My kids use the JW buzz words but prefer saying 'grace' instead of 'undeserved kindness', are comfortable saying 'Jehovah' rather then 'God the Father'
What is most important is that your child have firm foundational understanding of both parent's religion so that they may discern their own beliefs.
I am not saying there won't be bumps but it is very important for you adults to know how to disagree without getting emotional bent. When your daughter asks why doesn't daddy do Halloween yall can sit down together and have him explain his POV and then yours. From their yall can ask her opinion or have a pre-arranged compromise for her to accept (we attend a church sponsored fall festival where no horror costumes are allowed but has plenty of candy and games).
Church attendance can either be rotated each week, blended or observed all together.
If he does go back, there is nothing you can do (especially if you marry) to prevent him from involving her in WTS theocratic activities (just like nothing can prevent you from enrolling her in Sunday school).
Counselors can help you map out the middle ground in which yall will strive to dwell. Plan ahead to discuss the plan of action regarding blood, baptism, holiday participation, pledge of allegiance (my kids can choose holidays but the pledge is solidly not going to be said), college degree before inquiries of pioneering, pioneering versus peace corp, church and KH (kindom hall) participation (church choir and Theocratic Ministry School), community (or church sponsored) volunteering versus field service............ either trading things off or incorporating both POVs
You daughter will spiritually lean more toward her primary caregivers beliefs as she will be exposed to them more often.
(While I am very pro-marriage, in so many ways I would suggest postponing marriage until after he returns and begins to manifest his reactions to being back in the Troof)