I don't think any of us has any idea what constitues the idea of a dimension, so who are we to say what they are made up of, what they need to begin and such? As far as we know, any dimension doesn't have a beginning or end. Really, this makes Home a truly unique dimension, totally different from all others, wherein it HAS a beginning.
Now, CT argues with the theory of there being no beginning or end with the idea of the End of Time. I see the End of Time as being also the Beginning of Time, where there is nothing before the Beginning, and nothing after the End.
Take this into account with Home. And that's my reasoning.
Besides, why else would Lavos be able to survive simply because Serge is alive? What's he gonna do, go to the PD, kill Crono and Co, and make it so Lavos actually lived, thereby ridding the world of the new future and Chronopolis, thereby ridding the world of El Nido and Serge's birth?
Wow...I feel smart...or really stupid >_<