1. He'll set things straight before and he will do it again.
Where you said above: "*He'll set things straight before," I'm sure you meant to say "He set things straight before."
I think both interpretations are possible. Interpretation (2) might be a case of "excessive conciseness," so to say, but I wouldn't say it's wrong. Context can help, for example:
- When we bought this house, this wall was white. Then we painted it gray. Now we'll paint it white again. (Now we'll paint it white + As a result the wall will be white again.)