Delaying Tawaaf al-ifaadah so that one may do it when leaving

Yes, it is permissible to delay tawaaf al-ifaadah and then do one tawaaf which will suffice for both tawaaf al-ifaadah and the farewell tawaaf.
But it is better to do two tawaafs, one for ifaadah and one for farewell. 

Even better than all of that is to do tawaaf
al-ifaadah on the day of Eid, after stoning Jamrat al-‘Aqabah and slaughtering the hadiy (sacrificial animal), and cutting your hair or shaving
your head. Then when you want to leave Makkah, you should do the farewell tawaaf. This is what the Prophet (peace and blessings of Allaah be
upon him) did. 

Shaykh Ibn Baaz was asked about this matter
and he said: 

There is nothing wrong with that, if a person
delays tawaaf al-ifaadah and when he wants to leave he does tawaaf after he has stoned the jamaraat and finished everything. Then if he does
tawaaf al-ifaadah that will suffice for the farewell tawaaf as well. But if he does both – tawaaf al-ifaadah and the farewell tawaaf, that is even
better, but if he does just one and intends it as the tawaaf of Hajj, that will be sufficient.

 Fataawa Ibn Baaz,
17/332.