Salary in USA while working in India with no H1B status
It depends on your employer.
Legally, if you are not in USA on a valid work permit like H1B, your company cannot show you as an employee in their books and cannot pay you salary.
Since you will be completing your 6 years quota on H1B, your employer cannot show you as a legal employee.
They will probably pay you through a contracting company in India. Legally, your employer can hire a contracting company who internally can get work done from India.
Should I pay US taxes
The US taxation will come into picture based on your stay in USA in the relevant financial year. If you pass the substantial presence test from IRS, then, yes, you will have to pay US tax for that year.
Receiving Salary on my SSN while working from India
I strongly recommend to NOT receive any pay on your SSN while you are working from India after your 6 year H1B quota is completed.
You would be considered working in USA without any valid work authorization if you receive pay on your SSN from US company.
This may or may not be tracked by USCIS but it is best to avoid.
US SSN and Medicare taxes
If you do not get paid in US, there is no question of deducting SSN and medicare taxes.
Does that answer your question?