It is rare, but it is possible. After a while the cut ends can actually heal together. This can cause the sperm to be able to travel the normal route and result in pregnancy. And if the ends are not cauterized properly, sperm can leak into the scrotum and then into the other tube.
Yes, it is possible. On rare occasions, if the tubes were snipped and not properly cauterized, or a small section was not removed, it is possible that the ends can grow back together. There is another method of it occurring and that is called cheating.