There is no specific penalty under Excise rules for non filling of returns. But a general penalty of Rs. 5000 may be levied for non copliance with excise rules.
the invoice issued by the dealer may be cancelled, not hounoured by the department and he will face pressure from customers for reimbursement of excise duty for his non compliance with excise.
if the return is accepted by R/O with his seal and sign, then no penalty, but right now all dealers have to file the e return ( except in few cases where the dealer is importer)