well it's tough to say without knowing where the gasket is leaking. If it's allowing oil into the coolant, your car could last quite awhile as long as you make sure to drain and replace the coolant often (this will get expensive). If it's leaking coolant into the oil, the car will not last nearly as long because the coolant will remove the lubricating ability of the oil.
If you only need a car for 4 months, why not scrap this car, buy a $500-$1000 beater car, and drive it till it dies. You could get a late 80's, early 90's civic for that kinda money and it could potentially last until your kids are in college
