I think it'd be safer to suggest that Lavos will eventually come into being during the effectively eternal Quantum Reign that begins after the slow, torturous, freezing death of the universe.
When quantum effects are king, anything literally can and, theoretically, everything will happen!
Of course, that'd also mean that there'd be flying pigs, competent politicians, and Sephiroth... my, the sky is indeed the limit.
While it may be indeed possible that a planetary parasite is indeed infesting our planet from beneath the crust, that would be resting on a few other major assumptions, the greatest being that the Gaia concept (the planet has a lifeforce, which it may or may not share with us) is true.
Even if it is true, it probably won't affect us in the least. If we're talking about a being that has been sapping away the lifeforce of our planet for the last 65 million years, without any noticeable change in our planet's capability to bear life (think FFVII's spiel about what happens when enough Makou is removed), then that being probably won't emerge to rain destruction from the heavens while the human race still exists. We've been here for 100,000 years... those are tiny chances.
Besides, considering the crap that flies around in our universe, as well as the huge radiation effects, I'd say the wholesale decimation of the dinosaurs was "getting off light." It was the most common of common disasters, hardly anything so significant as a planet-eater. Who knows? A magnetar may be in our near future, and that would solve all our problems...
