Keep in mind that there is no rule about leaving lines and getting your spot back. Most people will be understanding, but if someone decides to block your way there won't be much you can do about it. Also, so lines are very hard to leave as they are designed so narrow that you have to push people to get by them.
I'm not trying to stress you out, but sometimes leaving a line and rejoining is easier said than done. I've hopped out of a couple (twice out of the Little Mermaid as the line just wasn't moving at all) and now I tend to look for the way out when I get in. Sometimes it is as easy as unlocking a chain or going under. Sometimes the only way out is to walk back the way you went in, saying Excuse Me the whole time.