I personally don't think the 1998 Lois and Clark will disappear. I think it would be more like the scene in Frequency where the room transforms around him and his dead parents are alive again.
I don't know how it worked in Frequency, but I guess I could go along with the idea that Present Lois and Clark live the next 3 years, then Future Lois and Clark (who, at that point, are at the very moment this story leaves off), have their world "transform" into Present Lois and Clark's future (now present).
