Yes, Smoking Zones and Areas are available at Mumbai Airport.
Terminal 1:
Between Departures Gates 1 and 2 at the check-in area of Terminal 1
Arrival Hall
Between Gates A6 and A7
Opposite Gate A3
Update: There is a good spacious smoking room after Gate no. 26.
Terminal 2:
Smoking area available near gate 42.
International Departures Smoking Areas – Post immigration:
Level 4, At the Retail area
Level 4, Near gate 68
Outside Terminals Smoking Areas:
Smoking is allowed at Designated Areas at Mumbai Airport, and Parking Area.