You can't undo the split. One of the caveats passed in the same vote states that you can't reduce housing density - so if you build two units, they can't be reunited into one lot again.
I'm assuming for future construction, you'd have to treat each lot as separate with regards to setbacks from the property lines. So no building a house that straddles the old property line, I suppose
Can't I just own and use both lots at the same time? Would I need to technically 'reunite' them? Can't I just use both of them at the same time?