Regarding Business

You must file ITR for AY 2019-20, if aggregate income above basic exemption limit. 

From next year your business (or income u/h.  'PGBP')  will be NIL, if business closed.

There is no requirement to intimate closure of business (if proprietroy).  The change is earlier you had business income to show in ITR and now you will not have business income to show as it's closed. 

But you would be having other sources of income so better you continue to file ITR even if taxable income is below basic exemption limit of Rs 250000/- .