JOEL - It has no effect whatsoever on what level in heaven the parents obtain. As we learn in the parable of the ten virgins(Matt 25), ultimately we are all individually responsible for our own salvation. It is true that if parents fail to teach and raise their children in the Gospel the sin will be upon their heads(D&C 68:25), but if they have tried their best, what their children ultimately decide to do has no bearing on the parents' salvation. Remember that even God lost one third of His own spirit children who wanted to have their names removed from His plan of salvation(D&C 29:36).
And while it is true that we can't be exalted without an eternal companion, if we have become the kind of person that deserves exaltation in heaven, God will find a way to make sure we get it.