Refund of accumulated ITC?

No.........................

If a person is having accumulated ITC in ITC ledger, then it means that person has stock of goods against which ITC balance is available.
So during closure of business, he will be selling those goods to buyer and he will be charging GST against same. Balance in ITC shall be used against the GST liability on account of sale of stock

if he sells all his stock under cost that time will he get

No, unless he is making zero date supply

As per Section 54 a claim for refund is arise on account :
Export of goods or services.
• Supplies to SEZs units and developers
• Deemed exports
• Refund of taxes on purchase made by UN or embassies etc.
• Refund arising on account of judgment, decree, order, or direction of the Appellate Authority, Appellate Tribunal, or any court.
• Refund of accumulated Input Tax Credit on account of inverted duty structure
• Finalization of provisional assessment
• Refund of pre-deposit
• Excess payment due to mistake.