just take it to a place who can fill the crack and see what they have to say,becuse if you leave it too long it will get worse in the bad weather, plus if you have an accident it will shatter.
If they can repair it , get it done as it would be a lot cheaper than replacing the entire thing, but if they recommend it being replaced due to a fault in the glass replace it.
I wouldn't wait around and hope it won't get bigger, and have the risk of being pulled by the police and being fined for it as well as replacing it!
The real art of conversation is not only saying the right thing at the right moment but also to leave unsaid the wrong thing at the most tempting moment. -- unknown