If you used BTC to buy anything that is considered disposal of the commodity and liable for tax at the time of disposal. If you did not report that disposal you are liable for tax evasion. If you mixed the BTC before 'losing' it then you have failed to maintain sufficient records of the commodity and would potentially be liable for deliberate concealment of your commodity holdings and failure to keep adequate records of those commodity holdings.

The only certain way to un KYC BTC holdings is to sell and report that sale to tax dept and pay the tax due. Then buy again via non kyc means.