He divorced his wife irrevocably then died during her ‘iddah

If a man divorced his wife irrevocably when he was healthy,
then he died during her ‘iddah, she should complete the ‘iddah of divorce,
not the ‘iddah of one whose husband has died. She does not inherit from him
and she should not observe mourning for him. 

For more details of that, please see the answer to question
no. 111905. See also
al-Mawsoo‘ah al-Fiqhiyyah, 29/325 

Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) was
asked: If the husband dies, having divorced his wife irrevocably, during the
time of the ‘iddah, should she observe mourning for him? 

He replied: The correct view is that she should observe the
‘iddah of her divorce, not the ‘iddah of one whose husband has died, and she
should not observe mourning for him. 

If the divorce occurred during his final illness but he died,
then she inherits from him, but she should not observe mourning for him,
because her inheritance in this case is not because she was his wife, but
because he wanted to deprive her of it, so he is to be punished by having
his plan thwarted. Hence if she died during the ‘iddah, he does not inherit
from her.

End quote from Thamaraat at-Tadween min Masaa’il Ibn
‘Uthaymeen (p. 116) 

For more information on the types of ‘iddah for a divorced
woman, please see the answer to question no.
12667 

And Allah knows best.