Die through his foolishness (6)
I believe the answer is:
perish
'die' is the definition.
(I know that die can be written as perish)
'through his foolishness' is the wordplay.
I cannot quite see how this works, but
'through' could be 'per' ('per' can mean through or by means of) and 'per' is located in the answer.
an anagram of 'his' is 'ish' which is located in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for perish that I've seen before include "Wither or die" , "Deteriorate, rot" , "Die; decay" , "Go off" , "Lose one's life" .)