If you're still employed, then, unless you're unfit for work or on leave, you should follow all reasonable instructions including to attend a meeting. If you are unwell, then the negotiations may be undertaken by email or other correspondence. If you don’t feel you can face the negotiations, or would prefer someone to deal with the key issues and legal jargon on your behalf, your solicitor can contact your employer, or their solicitors, if they have legal representation too. That is often a good way to ease the pressure on you and allows your adviser to cut to the key issues for you.