Only context can tell us exactly what it means.
He is on his way.He wrote a great book and now he's off to Paris to promote it.
Then there's, "We're off too see the Wizard, the wonderful Wizard of Oz", which was occurring at the time, hence present tense.
Yes, point taken. I meant that in this case, it was used for a present time event, as opposed to all of the previous examples, including your translation of "He is off to ..." as possibly "He will shortly be on his way", which is future 'tense'.We're off is always present tense. In your sentence, it's used to refer to a present-time event.
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