Is ITC reversal required if goods are sold below purchase price under GST

No need to reverse the ITC .

As per Section 15(3)(b) :Supplier can reverse his output tax on Discount given after supply only if :
(i) when there is any agreement before supply discount given can be linked to invoices.
(ii) when ITC on such discount is reverse by buyer.

So when both above conditions is satisfied & supplier has reverse his Output Tax liability then only buyer is liable to reverse ITC.

Note : Actually it is revenue neutral tax . supplier is reducing his liability & in same proportion buyer is increasing his tax liability.
Actually if we read the said section carefully we can interpret that It's just an option given to Supplier that if he fulfilled the said condition then he can reduce his tax liability. you can say that it is not mandatory to issue GST less discount credit note as there is no loss to government as it is revenue neutral.

There may be such instances where the gst needs to ve reversed but not in this case. reporting of actual sale value is a seperate thing altogether.