Market standard severance for managers?

I am a manager with ~18 years of experience with my company in Bangalore, a wholly owned subsidiary of an American company, and I have heard that they will shortly be doing a closure of their India operations and laying off all the Indian employees.

I wanted to get an idea of the market standard severance packages that are paid to manager level employees before going into negotiations with them?

What is usually offered? And what am I legally entitled to? Any other advice is greatly appreciated!