What is the court intended to accomplish?
Step away from your initial problem for a moment. What is your judicial system supposed to accomplish? Why do you have courts at all?
Some (real world) ideas that may be useful:
- Retribution: Criminals deserve to be punished. Punishment is not intended to “fix” problems, it is intended to punish people for wrong-doing.
- Restoration: Criminals should be confronted with their actions and repair the harm done. The idea of punishment isn’t as prevalent here, rather the focus is on fixing the effects of a crime (which may be more than material!).
- Rehabilitation: Criminals require some education, training, or support in order to stop committing crime. While there are likely some kind of punishments or penalties in place, the focus is really on making sure that the criminal doesn’t commit future crimes by providing them counseling, vocational training, and other supports.
Once you answer why you have a legal system at all, the answer will become a bit easier.
Applying that to your game
Now that you know in-game why the legal system exists you can make it work for you.
You’ve said your players have access to incredible wealth. This means they could trivially fix many material problems. However, a retributive justice system wold care very little – they are going to be punished for their crime even if they fix it. Additionally, the misuse of their wealth for criminal actions may make the punishment more serious.
A restorative approach to justice plays well to the PC’s strengths: they can pay their way out of many problems. But there are many intangible things which might be at stake, i.e. threats to individual memories, culture and legacy, a sense of safety and security. Wealth will help, but not fix, these problems.
A rehabilitative justice system will focus on the characters personal growth and teaching them not to commit future crimes. Wealth will not help. If they are found guilty, the players can’t buy their way out. They will have to undergo some kind of training or process to reduce their risk of not committing future crimes. You probably don’t want to RP out therapy sessions (or maybe you do, you avant-garde gm), but some terms may be more interesting to adventures. Consider the role of magical means to detect these crimes (like a court-appointed scryer, or a constant detect thoughts-type ability).
Your justice system will result in other effects across society. These will help answer some other questions.
For example, you also raised the question of how Wish spells and other magical things would influence crime and justice. However, the existence of your legal system will influence what is available and how available it is.
For example, in a rehabilitative justice system, people will to accept cash for an illicit Wish spell are probably few and far between. Once a spell-caster with criminal leanings is caught early in their career, they are rehabilitated. So although the rehabilitative system may seem soft in some senses, it also limits the help your PCs are going to get. There may simply be no one who can be bought.
You should also expect law to extend to the magical world. Sure, Wish can solve a lot of your problems, but not if spell casters capable of casting it are bonded, licensed, or monitored some other way. The law is probably monitoring those people – including your PCs.
Parting Thoughts: This is an invitation to you as a GM
As a parting thought, consider this challenge an invitation think about the fictional legal and political world that your characters inhabit. What do the people of your world expect from their legal system? Is it effective? How does it maintain fairness in the face of powerful magic? How does it make sure that judgments are implemented correctly? You’ll end up with a more interesting game world and more satisfying game experience.
And even if your players just go back to slaying dragons, you’ll know how to handle the inevitable problems about exporting the body parts of endangered species.