Not all management break-ups need end in high profile court cases - and most of them don't.
Some managers don't work with contracts. They might be a friend of the artist and have known them for years - in this case they prefer to rely totally on trust. However, you still have to work out how much a manager is paid for the work done. If it is decided that this relationship can't continue, financial arrangements will have to be sorted out to the satisfaction of both parties. If agreement can't be achieved and it ends up in court, you can expect that the legal profession will look at what is generally recognised in the music industry as the right pay for what's been done, and award payments in line with what is widely acceptable.
You can agree a trial period without any contract.
If you have a management contract then it should stipulate how long the relationship is for. This could be two to five years, though three years is the usual contract length in the UK. At the end of the contract, the two parties can agree to part or renegotiate.
When you meet a manager you can agree a trial period without any contract to see if you suit each other. Then at the end of the trial period you can either agree to part or formalise the arrangement with a management deal.