Generally a really bad intake manifold gasket will make a car run rough at idle and/or cause a service engine light to illuminate. If a mechanic diagnosed it when you were in for regular service, but you did not have a complaint then you should be fine.
As far as driving the car, as long as you don't have a fluid leak or the car is not stalling or running rough, it should be fine to drive for a few months. The car's engine management will adjust for small intake leaks to where you may not even notice the issue.
If the car runs rough or has fluid leaking out I suggest having the gasket replaced sooner than later to avoid the possibility of engine damage.