A personal loan is called as an unsecured loan which is a loan without any tangible security. In my opinion, following actions can be done by the Bank on defaulters.
Any account become NPA after a lapse of 90 days I.e. if your account remains in continuous overdue for 90 days then only Bank has the right to initiate any legal action against you.
If you always keep an overdue equivalent to 2 months installment in your account, Bank will just remind you by calling you and writing you to pay your EMI on time and then if you pay one month installment then they will not be able to do anything , they will again start calling you or your employer at the most, as check off facility got signed from employer in most of the cases i.e. your employer gives undertaking to deduct your loan installment and credit to your loan account directly (in some cases) or Bank can directly debit your salary account for overdue installment, if you maintain your salary account in the same bank.
Apart from all above, assuming that you have left your job Or you do not maintain your savings Bank account with the Bank and you have defaulted for 90 days then Bank can initiate legal action against you.
Bank also appoints recovery agent.
Bank can use the Post dated cheques you have submitted and return of cheques due to insufficient balance is a criminal offense under Negotiable instruments act.
At the max, you will be summoned a legal notice and thereafter you will be liable to face court proceedings.
Bank also approaches for settlement of loan as well , in which you can compromise your loan account on mutually agreed terms but it will affect your CIBIL score a lot and your future credit worthiness will get affected.