The lease agreement speaks the terms and conditions agreed between the tenant and the landlord. If the tenant breaches the conditions lease agreement by vacating the premises without giving notice as mandated and agreed in the agreement he has to aide by the condition agreed to the deduction notice period penalty from the earnest deposit and also for the damages to the house property during his tenure of stay as tenant.
can tenant file a case against owner ?
Even if files a case it will not be maintainable because he has agreed and signed the lease agreement to abide by the conditions thereon, so need not worry.
Will flat get seized.
No, not at all, why do you get such doubts, who confused you this way?
Can flat be rented out to someone else?
Yes, why not. you can proceed with a new tenant, there is no restriction to it.