That is my concern too. If there are no service areas available, we would need to get off from the Motorway for Petrol and then get back on it such as Multan interchange.
I think once you have refueled your car from Multan with full tank, you can cover M5 upto Sukkar with 40 liter tank (assuming your vehicle has 40 liter or bigger tank). My vehicle does more than 450km on full tank too. Another possibility is to have jerrycan for additional fuel as an emergency measure but I don't recommend it since I it could be a safety hazard.
By the way, Is there any service area on M4?