H1B approved but cannot join employer

[mapleleaf_1]

Guys,

My H1B is approved in 2014, not yet visa labeled, but I can not join the employer. I have a better offer from NSW, AU and would like to continue here only.
My questions are as follows.

1. What will happen to H1B approved petition if I do not use it?
2. Do I need to pay anything to my employer? If so, how much?
3. I only signed an acceptance letter but no contract. Am I legally obligated with the employer for anything?
4. Will this impact me in future should I decide to travel later to US?

Edit - I am currently living out of USA.

Please suggest..