It’s a fair question. Steve Jobs is legendary. Steve Jobs was the man. Steve jobs helped transform Apple into what it is today.
<Pause> Lest you worry that this is another worship-Apple blog entry, let me assuage your fears or crush your hopes (depending on which side of the digital fence you are on). While I do think Steve Jobs did a lot to transform Apple into a superpower of sorts, I think giving him all the credit is unfair to the thousands of Apple employees who work hard each day to keep Apple ahead of the curve.
<Play> Apple will be just fine. 
If Apple falls apart in the coming years it will not be because Steve Jobs is missing from the helm. Apple has loads of cash, a brilliant creative team, established history of success, good supply chains, and an extremely loyal fan base to name a few reasons they will be around. There are plenty of companies that succeeded when their iconic founder(s) passed away. There are also plenty of companies that went under when their iconic leaders passed away.
I’m willing to bet that Steve left a phenomenal succession plan in place to make sure Apple was ready to go without him. He will be missed.
If the Apple does fall from the tree of glory because its incredible leader is gone then I put forward it wasn’t a very good company to begin with. For if a company hinges upon a single man (or woman) then that company is destined to fail.
A lot of people look at Tim Cook as Steve’s successor and wonder how could he replace Jobs. Cook picks up the administrative aspects of Steve’s leadership, but don’t forget that no one at Apple had more power than the designer Jony Ive. Apple is driven largely by design, so Ive will doubtless keep Apple aligned with Steve’s vision as they bring his remaining brainchildren to light over time. But what IS Apple going to do with $70B in cash? Space travel, anyone?
Nanobots? You have to believe something big is ahead.
I agree that they won’t “go under”, but he was so rare and so exceptional that I don’t think they’ll ever be the same company they were before. For one, his rock star status opened doors that no one else at Apple will ever be able to open (take for example his deals with recording artists, no one else could have had an open door with Bono and the Rolling Stones like he did). Second, his absolutely genius at filtering out the unnecessary and focusing like a laser beam on what was important is unparalleled and simply can’t be replaced by another “great leader”. What happened to Apple the first time Steve Jobs left will inevitably happen again, I propose. It just might take a few years longer this time around.