He would go back in time and access Mortis itself and become a universal God, then continue to spread across all the timelines for Eternity, forever conquering.
__________________ "Vader's pulse and breathing were machine-regulated, so they could not quicken; but something in his chest became more electric around his meetings with the Emperor; he could not say how. A feeling of fullness, of power, of dark and demon mastery -- of secret lusts, unrestrained passion, wild submission -- all these things were in Vader's heart as he neared his Emperor. These things and more."
The future IS always in motion to a point, and that may be why Yoda was cautious of relying on future sight while he was alive -- it was too difficult to see what the one true line/future would be.
But the existence of TWBW does tell us that all the events in motion do ultimately culminate into fixed events. Time isn't linear. That's why Ezra was hearing voices/quotes from characters in the OT and ST films(which are obviously set after Rebels) once he entered that realm. The implication is that Force spirits also perceive all of time simultaneously.
As for the thread: Palpatine would alter time in such a way that defeating him would literally become impossible. He'd then set his sights beyond the mainstream galaxy, and conqueror the entire known universe(that was his primary goal anyway.)
__________________
"I am tired of Earth. These people.
I am tired of being caught in the tangle of their lives."
Iirc that was said in Tarkin. He found Plaguies obsession with immortality fruitless and what he really wanted was to basically achieve Omnipotence and rule the Universe 4 ever.
__________________ "Vader's pulse and breathing were machine-regulated, so they could not quicken; but something in his chest became more electric around his meetings with the Emperor; he could not say how. A feeling of fullness, of power, of dark and demon mastery -- of secret lusts, unrestrained passion, wild submission -- all these things were in Vader's heart as he neared his Emperor. These things and more."
"And [Palpatine] would not allow himself to be sidetracked from his goal of unlocking the secrets many Sith Masters before him had sought -- the means to harness the powers of the dark side to reshape reality itself; in effect, to fashion a universe of his own creation. Not mere immortality of the sort Plagueis had lusted after, but influence of the ultimate sort."
-Tarkin
__________________
"I am tired of Earth. These people.
I am tired of being caught in the tangle of their lives."
See, when reading this and the stuff with the world between worlds, Palps being the final boss for the ST trilogy I wouldn't have minded. Just needed to be better executed.
__________________ "Vader's pulse and breathing were machine-regulated, so they could not quicken; but something in his chest became more electric around his meetings with the Emperor; he could not say how. A feeling of fullness, of power, of dark and demon mastery -- of secret lusts, unrestrained passion, wild submission -- all these things were in Vader's heart as he neared his Emperor. These things and more."