Does saying "be right back in 1 hour" mean I'm going to be back in 1 hr? or does it mean I'm going to be gone in 1 hour?
It means that the person will return in an hour – although such a casual expression may indicate that the person could be away longer than that. Or less time ...
But it definitely does not mean that the person intends to leave in an hour's time.
It means the person will return in one hour. I agree with Livrecache that chances are that the person will take longer than an hour, but he's giving the listener an idea about when he will return.
"Be right back in 1 hour": It means within 1 hour, not exactly 1 hour (20 minutes, maybe...)
"I'm going to be gone in 1 hour": exactly 1 hour
That's an example of Internet slang, but not strictly though. Be back in one hour is simply a shorter way of saying I'll be back in one hour which means that the person will leave and after one hour they're going to be back. I'll is left out because that way the thinking goes it's "supposed" to be faster to type things into your computer when there are fewer symbols in a sentence. You see this used a lot mostly by people who make use of instant messaging apps to text each other over the Internet.