I am planning to go to Nepal but dont know when i would be able to return. Its cheaper to get return ticket than just one way. But i am not sure if open ticket option is available. when i asked travel agents there is no open ticket system anymore. Do anyone of you know or share any information. I 'll appreciate any information.

 Open ticket isn't an option. 

You can buy a ticket with less restrictions - eg., one change allowed. Or you could pay a little extra that allows you to make changes twice. I guess it's close to the ticket being open.