Rule 43 will not apply here since it is not a case of using capital goods for taxable and exempt supplies. What applies is Section 18 (6) of the CGST Act' 17 r/w Rule 40 (2) of the CGST Rules' 17. Accordingly, you have to pay GST of - (i) 20% of ITC taken (since 4 years old) or (ii) 28% on the invoice value (which shall conform to sn. 15), whichever is higher. You have to pay GST even if it is sold below WDV price, as per the said provisions.
Sn.18(6) -- In case of supply of capital goods or plant and machinery, on which input tax credit has been taken, the registered person shall pay an amount equal to the input tax credit taken on the said capital goods or plant and machinery reduced by such percentage points as may be prescribed or the tax on the transaction value of such capital goods or plant and machinery determined under section 15, whichever is higher:
Rule 40(2)-- The amount of credit in the case of supply of capital goods or plant and machinery, for the purposes of sub-section (6) of section 18, shall be calculated by reducing the input tax on the said goods at the rate of five percentage points for every quarter or part thereof from the date of the issue of the invoice for such goods.