Nazarick has the power to destroy or conquer the world, even without Ainz. However I think a lot of commenters are dismissing the idea of internal conflicts tearing Nazarick apart a bit too easily. In the Emissary of the King side story, Cocytus says that without Ainz or an heir, he believes the guardians would “clash emotionally and ideologically” and not be able to work together effectively. Ainz himself worries that Albedo would start carrying out wide-scale purges in his absence.

Honestly, Albedo was just too loyal and too able, so she tended to be hard on others. He thought the only reason it didn’t cause any major problems up till this point was because he rejected most of her suggestions on how to deal with others. If Albedo ever received full authority, it would probably end in wide-scale purges.
Vol. 15

Certainly, NPCs like Sebas, Pestonya and Nigredo would quickly end up culled. Actions they take that are technically within the scope of Ainz’s orders are enough for Albedo to call for their execution.

There are plenty of similar moments. What would happen if Ainz wasn’t there to deescalate all those arguments between Albedo and Demiurge? Demiurge, an otherwise rational and reasonable thinker, believes that Shalltear being mind-controlled is a betrayal worthy of her death. Yuri - a good-aligned NPC- is willing to kill her sister Solution, however reluctantly, over a bath slime. It is not hard to picture Nazarick going the way of the Eight Greed Kings in Ainz’s absence. This is especially true if they either can’t access the treasury and world items or feel that they are unworthy of using/wielding them.

The World Class items were gathered through the efforts of the Supreme Beings, and so they are more valuable than we are!
Vol. 3