Well first he would have to deal with The Vong, since he sensed them as far back as the Clone Wars. But after that, pretty sure that's been said a few times already, become an omnipotent being and go after other galaxies or something.
__________________ "Imperial troops have entered the base! Imperial troops have entered—"
―Jobin, warning Echo Base' stragglers of the snowtroopers' advance
Registered: Jun 2016
Location: At the forefront of Sheev's armies
The Emperor planned to assimilate the galaxy into his ego, controlling everything and everyone within it, becoming more of a force of nature than an individual being: he would literally become the galaxy. After that he would journey to other galaxies and do the same, as a sort of expansionist entity hellbent on absorbing all of existence into his being. Once the his very name was synonymous with the universe and he would have replaced the Force as the energy field that controls the fates and destinies of all beings and rules of the laws of nature, he would presumably seek to go interdimensional and conquer all the known realities until total and complete omnipotence was attained.
__________________ "I created Azronger in a laboratory. He is Sheev's chosen vessel." - The_Tempest
The Rule of Two was a problem solving system, not a directionless pursuit of power. It was the solution to ending in-fighting and destroying the Jedi once and for all. The founding tenets of the Sith themselves didn't change.
This is elementary stuff.
__________________ “The galaxy must experience the pain of death and the rapture of rebirth as I have. I will bring chaos. It is time for war.”
Can you sources that discuss this? I know the Dark Empire endnotes talked about it.
__________________ "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."
Registered: Jul 2015
Location: The Darkest Corner of your Mind
I just don't find his motives very interesting. Dooku was a political idealist, Vader originally did it to save the ones he loved, Xizor was a materialistic womanizer, Thrawn legitimately enjoyed what he did as a pragmatic, logical person who enjoyed the structure and order the empire brought to the galaxy, the list goes on.
I don't know much about Valkorian, but I'm assuming he too had similar intentions?
To express my question in a another way, here is a similar one from stackexchange:
Let's say that a Sith Lord achieves all of his goals and becomes the ruler of the galaxy (similarly to, for instance, what Palpatine managed to).
Also let's assume that the Sith has killed all the remaining Jedi and has repressed any form of rebellion. It has achieved a state where he has total political control through fear.
On a rather more personal note, he is a being with formidable powers. He basically cannot be defeated in combat since there are no other trained Force users, and his extraordinary abilities cannot generally be matched in a 1-on-1 combat.
On this point, what kind of driving purpose could this Sith have in his life? War is over, fighting and killing seems unnecessary, unless it would do it for fun, which doesn't seem to characterize the Sith though.
What kind of pleasure could he take out of life?
What would he do with the accumulated power? What move "evil" purposes could he start cooking?
As with most of my answers on here, I'm going to lean fairly heavily on Legends, as the philosophy of the Sith isn't built out very well in the new canon.
According to the Sith Code, the ultimate goal of the Sith isn't power or domination, but freedom.
Peace is a lie, there is only passion
Through Passion I gain strength
Through Strength I gain Power
Through Power I gain Victory
Through Victory my Chains are Broken
The Force shall Free me
The Sith are all about using power and victory over opponents and obstacles as a vector to personal freedom. The core of the Sith ideology is that any limit imposed on you that inhibits your ability to do what you wish is a shackle, and the only way to break those shackles is the accumulation of power and the domination of anyone who gets in your way. There is no after for a Sith.
Ruling the galaxy isn't actually the goal--nor is defeating the Jedi; both are simply a means to the ultimate end which is, as the Sith code so succinctly states, Freedom.
So let's look at some specific examples like Sidious or Vitiate, who accomplish most or all of their Galactic Domination scheme. They both get close enough to the point you're talking about to be relevant behavior studies. Both Emperors are the unabashed masters of their domain (for a time,) and are functionally unchallenged (for several years, at least). Once that happens, they both turn to conquering the ultimate chain: Death.
Death is seen by the Sith as the final failing of the Weak (expressed as such various times in SWTOR dialogue, KOTOR/II, Darth Bane, Darth Plagueis, etc). To die is to be ultimately powerless, to have your will so thoroughly overridden that you can never hope to express it again.
Logically, then, most Sith Lords atop massive power structures with nearly unlimited power at their fingertips start looking into ways to prolong their life indefinitely; ways to avoid that final failing and ultimate expression of weakness.
So a few quick summary points:
Galactic domination isn't the goal, it's a means to an end
The Sith Code posits that freedom from any restriction is the ultimate goal
A Sith with nearly unlimited power really only faces death as a restriction on his action
So most Sith who 'Win,' as it were, spend their time trying to become immortal.
__________________ "When something is important enough, you do it even if the odds are not in your favor." - Elon Musk