The world wins. A bunch of 10th-level characters have plenty of means to locate and destroy the wizard. The wizard must anticipate and foil every single one of these attacks. One mistake--and everyone, even a 20th-level wizard, makes mistakes--spells death.
You know, unless the wizard is smart and plays the long game. . .
Resources are no problem, due to True Polymorph letting you get permanent access to gold. This lets you get every spell in your spellbook, giving you infinite versatility and resources. Using these spells, you're going to build a dungeon/fortress that serves the second purpose of luring in your enemies and killing them with death traps. Telekinesis, True Polymorph, Stone Shape, Transmute Rock, Disintegrate, and many other spells will help you in building this fortress/dungeon.
Get a bunch of Glyph of Wardings set up in a base, especially one that lets you teleport if they somehow do become a serious threat. The party of rebels will be facing a ton of spell-slot free fireballs, dominate person, 9th-level bestow curses, finger of death, and any other nasty spell that will seriously annoy/destroy your intruders. You can use necromancy spells to create pits/rooms of zombies and wights, as well as skeletons hidden behind arrow slits to shoot unsuspecting enemies while being mostly out of reach.
You can even make Eyes of Fear and Flame, Frost Giant Zombies, Gnoll/Blood-Drinker Vampires, Phylaskia, Shadow Assassins, Sword Wraith Commanders, or a T-Rex Zombie with True Polymorph. Undead don't need food or water, and will willingly do your dirty work in order to kill the living. Other minions can be created by using True Polymorph on an object to make a Clay Golem, Frost Salamanders, Myrmidons, Abhorrent Overlords, Adult Oblex, Cloakers, Ulitharids, Grey Slaad, Mind Flayers Scaladar, Living Blade of Disaster, Warforged Titan, Vampiric Jade Statues, or any other CR 9 or lower monster (preferably immortal ones).
Have your base be a maze, with dozens of
dead ends that can kill party members with traps, spells, and minions. You can disguise your traps and create false traps with Nystul's Magic Aura, create elaborate puzzles using Glyph of Warding, and punish those who dare enter the dungeon with tons of illusions and other tricks. (For example, a dead end room that looks like it would move on to the next area, but is actually a death trap. The floor is made completely of stone, but a glyph of warding is set that uses transmute rock to transform the ground into mud. Underneath the ground is a huge pit trap that you carved out using disintegrate.
Adventurers can't resist a good dungeon, and you need to make yours more drawing and deadly than the Tomb of Horrors.
Smart wizards can kill their enemies even before they reach them if they use enough ingenuity and magic. Once enough of your enemies dies, others will hopefully either bow to your rule or go in hiding, allowing you to easily conquer the world, using threats of unleashing an army of dragons (created with True Polymorph and raised by you), Meteor Swarms stored within Glyphs of Warding that would utterly destroy a city upon your command, or brutally slaying the ruler/champion of a large kingdom, using Major Image to show this graphic death to the members of the kingdom. Once you get charge of one large kingdom, you can go on conquering all other nearby nations, using the same tactics of conquering them as before.
A level 20 Wizard can easily take over the world if given enough time.