I was contacted by my employer during my medical leave from work and was offered a retirement allowance. Can I switch from EI sick benefits to EI regular benefits when I recover from illness?

EI eligibility depends on whether you have enough insurable hours to qualify and, if you are off for too long on a medical leave, you may not qualify once you have recovered. You should contact Service Canada directly to discuss how your entitlement to EI would be effected, as they are ultimately the department that will make that determination.