Hi,

I came to Germany on 14-July-2013. I got a job and got EU Blue Card which is valid from 05-Sep-2013 till 4 years.
After few months, I got pregnant and started my Mutterscahft on 18-July-2014. 

My Elternzeit will end on 27-Aug-2015. During my Elternzeit, I have decided to stay outside of Europe.

Can I change my job after my Elternzeit is over ? Same EU Blue card will still be valid ,right?

With any valid german Visa you are allowed to be away for a period of 6 months as far as I know. How long have you been away? If you are away for more than 6 months please check your validity of the visa before travelling back to Germany. 

You can definitely change your job after elternzeit. But you have the job protection law which means you could go to the old job and your boss MUST employ you (provided your contract was long enough and didn't end during your mutterschaftzeit.)