Well, I know quite a few people who didn't do that well in their HSC... and now they are heaps loaded and successful. My uncle, for example, didn't do that well in his HSC, only has HSC as his qualification, and is now a managing director of a company, drives luxury cars (which he changes/buys every few months lol), has a MANSION near the water.... and he's lovin life.
Don't think the HSC is the end of the world... really.
BUT, in saying that...
If HSC is going to be the qualification you rely on.. then it will not be a good thing when your employer sees it (considering you're HSC is pretty poor).
Then again.. if you eventually get a degree, or some sort of certificate or diploma at TAFE/college, I'm sure your employer will be more interested in that, than your HSC.
Again, I still don't get when people say that "ohh I screwed up my HSC, but like i'll do some sort of alternative pathway into uni"... when they weren't competent enough to gain a good HSC in the first place (unless of course there were bad circumstances - health, other issues etc).
Meh, that's my two cents.