If your personal assistant decides to leave then they need to give you notice. The amount of notice required will be in their employment contract and should give you enough time to employ a replacement personal assistant. It might be a good idea for the new PA to meet the person who is leaving, so they can talk through how they did things for you.
You must inform your self-directed support team at the Local Authority immediately so that the necessary adjustments can be made and the Inland Revenue updated.
You should make a note of whether any annual leave is owed to the employee. Once all payments have been issued, the employee will be issued with a P45.
Give your personal assistant any certificates they may have achieved through any learning and development completed, whilst employed by you.