I think, it will be done in one tank quite easily.
Just to give u the example:-
I recently went on Nissan AD which has a bit smaller tank (around 35 L) and consumption is quite higher than City. I topped up from Abbotabad and near Chilas its fuel gauge was a bit less than half (however, i got the tank refilled again). On way back, i filled the tank at Gilgit. Took same route i.e.via Babusar, Naran etc. And I utilized the 10L reserve petrol to refill even after crossing Haripur.
Actually on way back, from Babusar till Haripur, it is mostly downhill slope and resultantly, fuel consumption is very very less.