Intimation u/s 245 it

An individual assessee filing returns has received an intimation u/s 245 stating the following

Refund of Rs. 6136 for AY 2009-10

Demand of Rs. 2446 for AY 2006-07 and Rs. 642590 for AY 2008-09

After going to all the documents and 26AS, there does not arise any tax liability.

Two questions:

This assessee is no more. Will his son, the legal heir, be able to reply to the IT dept?

Can the son reply u/s 154 rectification of assessment?

Thanks