One person does not make a huge impact to a company as large as apple. Their success is not going to be determined by the lack of Steve Jobs. Apple's success will be determined by the products that they sell. They currently dominate the market in about every technological good that people want.
Apple is going to do just fine without Steve Jobs. It is true that Jobs was the mastermind behind Apple and that he helped get Apple where it is today, however, he is not the only person that works there. Apple fans are very loyal to Apple. They will continue to be believing it is a better product than others out there in the market.