Only way to fix cracked glass is to replace the pane. And as Brian said, for a 10g, it's easier to replace the whole thing. You could get the glass and silicone cheaper, but you will spend a lot of time and effort cutting the old sealant out, replacing the pane, prepping the seam, sealing up the new seams, waiting for it to cure, testing to make sure the sealant cured properly, etc...That amount of time wouldn't justify the savings for most people unless it's a large tank.
Or convert it to a terrarium. But then you'd still need to get a new tank for your fish.