If an earth-like planet was slowed down to very nearly match its orbital period, so that instead of being tidally-locked to its star, the planet effectively had an immensely long day. Akin to Mercury's orbital resonance, albeit a more extreme case. Alternatively, as was asked here, what if a tidally-locked planet broke out of its synchronous rotation?
I am aware that in both cases the massive amount of energy needed to either slow down or speed up the planet, would probably decimate everything on the planet. However, if this happened gradually. Would the habitable zone/belt associated with most tidally locked earth-like planets be able to migrate slowly across the planet?
If so, how wide would the belt need to be, and what would be the maximum rate at which it could potentially traverse the planet?