Is it permissible to complete the circumambulation (tawaf) on the upper floor and drink Zamzam water during the farewell circumambulation (tawaf al-wadaa')?

If the reality is as described, then your Hajj and circumambulation are valid, and there is no fault in your circumambulating the seventh round on the upper floor of the mosque, nor in the separation between it and the first six rounds by prayer, drinking, or speaking.