He wants to leave Makkah then come back to do the farewell tawaaf when the crowding is less severe

It is not permissible for any pilgrim to leave Makkah before
performing the farewell tawaaf. 

Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) was
asked: Is it acceptable for those who live in Jeddah to leave Mina and go to
Jeddah without performing the farewell tawaaf, then come back a few days
later to perform the farewell tawaaf? 

He replied: 

It is not permissible for the people of Jeddah or anyone else
to go back to their cities before performing the farewell tawaaf, then come
back to Makkah when the crowding has become less severe. They should not
leave Makkah until they have performed the farewell tawaaf, because the
Prophet (peace and blessings of Allaah be upon him) said: “No one of
you should leave until the last thing he has done is to circumambulate the
House.” And Ibn ‘Abbaas said: The people used to depart from many locations
(within Makkah), but the Prophet (peace and blessings of Allaah be upon
him) said: “No one of you should leave until the last thing he has done is
to circumambulate the House.” 

Majmoo’ Fataawa Ibn ‘Uthaymeen,
23/353. 

Even if he comes back after that to perform the farewell
tawaaf, it will be of no benefit to him. Shaykh Ibn ‘Uthaymeen said: 

If he leaves Makkah
heading for Jeddah, and reaches Jeddah, then even if he performs it (the
farewell tawaaf) it will be of no benefit to him, because he left, so how
can it benefit him after he has left? 

Majmoo’ Fataawa Ibn ‘Uthaymeen, 23/353.