hrm. In the original time line, Schala didn't use her magic powers. The Pendant lost it's glow over time as it relied on the Mammon Machine to re-power it.
The planet awoke when Lavos appeared in the original time line just before Melchior, Balthazar and Gaspar were about to be dispatched by Lavos at Queen Zeal's command for speaking against her thirst for power. I believe the Planet knew that these three would be essential for Lavos to be defeated, as they are the only three who could assist Crono and Co. enough to make a difference.
Melchior was needed to create the Red Knife, which became the Masamune, and was needed to reforge the Masamune, which Glenn wielded against Magus, otherwise the team would have been defeated by him. Melchior was also needed to forge the Rainbow Weapons.
Balthazar was needed for his Epoch and to explain how to traverse Death Mountain to bring Crono back.
and Gaspar was needed in the End of Time, to guide Crono and Co. the most in their quest by giving hints of where and what to go and do next, to create the Time Egg which saved Crono, and to introduce the team to Spekkio.
Some of you seem to forget that Schala was needed in the Ocean Palace not because of the power of her Pendant, but because of the magical powers that she had aside from the pendant, that even Queen Zeal respected.
I think it is safe to say that the events in CC would have happened in any given outcome from CT, except for defeating Lavos at the beginning of a New Game+, or by defeating Lavos in the Ocean Palace, because those are the only two endings which result in the Debug Ending.
For the sake of a sequel, the planet could not prevent this from happening, but it could prevent a lot of the other tragedies from occurring.
The portal opened for Marle/Nadia in part due to the combined remaining energy of the Pendant and the Teleport Machine that Lucca had created, but the portal was there in the first place because of the planets' will, knowing that by sending Marle to the past, it would spur the events that happened after. Lucca was the only one since the Kingdom of Zeal that could possibly create a 'Gate Key' that would open those portals at will, so even with the 'others' that Gaspar remarked upon having accidentally stumbled through a gate and having to help them return to their times, Crono and Co were the only ones that had all of the skills on hand, and through their journey, aided by the Guru's, to defeat Lavos.
It all comes back to the Planets will for survival.