I am not a lawyer. You may seek professional help on this matter...
1). So if my H1B will Canceled and i will go back to india after that my parents become citizen and filed my green card so will anything related my H1B be affect me or not?
2). Should i have to inform to INS or US Homeland Security or my employer when leaving USA if i want to come back to USA once my parents became citizen?
3). If H1B will cancel then how many days i can stay in USA ?
Not defined in law. 2 weeks - 4 weeks are reasonable.
4). And will My Employer inform me legally by giving some papers regarding the cancellation of H1B?
Not necessary. But you may ask him for it
5). I read all the messages for ariesbkk18 for the complaint to DOL so what is the procedure.... Is it expensive ? What kind of documents do i have to produce to DOL?
I'll not recommend it. Try to settle with employer.