Once you lose sync you're fucked pretty much lol; I had my draenei twins lvling in redridge...pulled a few more gnolls than I could handle, ended up losing one and the 2nd barely survived with a sliver of hp, so he got a bunch of exp the 2nd didn't; and my lowbie boomkins are like 10k+ exp apart, basically too much work to get 'em back together; you can attempt to ungroup them and try to even them up but honestly, it's not worth the effort. just keep them more or less close to each other :p