It's a bit complicated, but the answer is it is sort of possible for anyone who is dead and didn't have their ordinances done to get to the highest kingdom. Mormons famously baptize dead people, they also do other ordinances for dead people. The belief is that it allows the dead person to then accept or deny the ordinances. They believe that in the afterlife before resurrection there is still the opportunity to be taught the Mormon gospel. That combined with someone doing your ordinances for you and you're good.
They believe dead people are doing missionary work to other dead people in the spirit world before resurrection (which I think happens after the second coming). I've heard that the second coming won't happen until everyone (alive and dead) has had the opportunity to accept the Mormon truth.