Assume that the Son was the first of the Ones to die on Mortis. A great shift towards the light would occur.

If this occurs, I would imagine that Sidious would panic, at least at first. He would sense the shift, but remain unaware of the cause. He would think that his plans, an entire millenium of plotting by the Sith, are significantly less possible to achieve. It would be far more challenging to destroy the Jedi and the democracy of the Republic. There was no contingency plan in place for such a situation.

When Anakin returns to Coruscant after his misadventure on Mortis, he would tell Palpatine all about the Ones and the planet. After Anakin leaves the Chancellor's office, Palpatine smiles sinisterly. His foiled plans, which were a great loss, have now become a very powerful opportunity.

Sidious would travel to Mortis and discover the well of the force. Never before has the Dark Lord of the Sith felt such strength. His new goal: take the place of the Son!

Upon Sidious's arrival to Mortis, he would encounter the Daughter. She would explain to Palpatine that the Force must be in balance. He would follow her ideals, for now... The daughter reveals that she knows what Sidious desires. She knows that Sidious wants the power of the dark side that Mortis has to offer. In order to claim it, however, the Daughter tells Sidious that he must pass a test: he must prove his abilities in the force to the Father and Daughter. Sidious agrees to the trial, but the results of the test remain unknown.

What do you think? Would Sidious be able to assume the Son's power? Would his original plans to conquer the galaxy be easier with his new strength?