An employee quitting on the spot can cause serious problems for any business. Firstly, you should check their contract, as you may be able to make a court claim if you have incurred extra costs as a result of them not working their notice.
You should also ask the employee if they’d be happy to provide an exit interview so you can understand the reasons they left abruptly. If there is an issue you’re unaware of, such as bullying or harassment in the workplace, this could affect your court claim and cause problems for your business down the line.