Can i get benefit u/s 80C

No, legal heir can not get benefit.

Also if FD is encashed in Apr, it is better not to clear it in 80C for Prev FY

See, legal representative wants to take 80C benefit in ITR of deceased. 

You can take benefit in AY 21-22, but you will have to reverse that in AY 22-23, as you have withdrawn the FD

Agree with above comment

WHEN THE FD WAS INVESTED, INTEREST INCOME ACCRUING FROM FD WAS SHOWN IN INCOME FROM OTHER SOURCES .
NOW ON MATURITY EITHER THE SUM OF AMOUNT CAN BE RE-INVESTED OR If not credited into respective savings account of the individual account maintained at bank.Now this amount is taxable with respect to increase of the exemption limit as such.
Now the date of maturity is pertaining to the relevant previous year in which it has matured.