He forgot to do tawaaf al-ifaadah and he went back to his homeland and could not return to Makkah

Firstly: 

Tawaaf al-ifaadah is one of
the pillars or essential parts of Hajj, and the pilgrim cannot exit the
final stage of ihraam except by doing it. Based on that, your uncle is still
in ihraam so several things are required in his case: 

1 – He must refrain from
intercourse until he has done tawaaf al-ifaadah and exited the final stage
of ihraam. If he had intercourse when he did not know that he was still in
ihraam, he does not have to do anything, but he must refrain from
intercourse from now on. 

2 – He must go to Makkah
and do tawaaf al-ifaadah. It is mustahabb to go to Makkah for ‘umrah, then
when he has finished ‘umrah and shortened his hair, he should do tawaaf
al-ifaadah. This is so that he will not enter Makkah without ihraam. 

See: Majmoo’ Fataawa Ibn
‘Uthaymeen (23/194). 

3 – With regard to tawaaf
al-wadaa’, if he does tawaaf al-ifaadah and leaves Makkah immediately after
that, this tawaaf will suffice for both tawaaf al-ifaadah and tawaaf
al-wadaa’. 

Secondly: 

It is not permissible for
him to appoint someone to do tawaaf on his behalf, because tawaaf is a
pillar of Hajj and is not a matter for which one can appoint a deputy.  

But if he is unable to go
to Makkah, because of sickness or because he is financially unable, then
some of the scholars regard him as coming under the same heading as one who
is prevented from proceeding with Hajj. So he should slaughter a sheep where
he is and distribute its meat to the poor and needy. Thus he will exit
ihraam and will not have to do anything more after that. But if this was the
obligatory Hajj of Islam, then he still has to do it, because this Hajj was
not completed. Whenever he becomes able to do Hajj, it is obligatory for
him. 

Al-Ramli said in his
commentary on Asna al-Mataalib (1/527): From the concept of the one
who is prevented from proceeding with Hajj, al-Buqayli deduced that if a
menstruating woman did not do tawaaf al-ifaadah, and she could not stay
there until she becomes pure, and she went back to her homeland when she was
still in ihraam and did not have any money and could not go back to the
Ka’bah, then she is like one who has been prevented from proceeding with
Hajj, so she should exit ihraam by means of making the intention, offering a
sacrifice and cutting her hair. End quote. 

Something similar is said
in Mughni al-Muhtaaj (2/314) and Nihaayat al-Muhtaaj (3/317). 

And Allaah knows best.