Severance Pay

i have been off work for over 12 months due to health problems, i have been to see a doctor appointed by my company and i am waiting to hear the outcome, i am not fit to go back to work and i am of the opinion that my company will terminate my employment due to illness. Can anyone tell me if they can finish me and what severance pay i will be entitled to, i have worked for the company for 13 years in total but left after 5 years for a period of 5 weeks but went back for a further 6 years i am only 3 years of retirement,