Severance pay is not necessarily a matter of “professionalism” or “accepted practice”. It may be a legal/ halachic responsibility depending on the job. If this is a practical question, check to see if your contract has any rights in this regard. Also if it is a clear industry wide standard that may give you rights. (For example in the Yeshivish Chinuch world it is generally accepted to pay one month’s salary for each year that you worked as severance pay for those who have worked at least 3 years before being let go. Bais Din will often enforce this.)