The only person suitable to take over from Boris is Rishi Sunak, but despite his qualities I fancy for such an inexperienced top line politician leading the UK out of the mess Boris has created will be too much for him.
If Brexit really is a complete disaster, they may not want a Brexiteer anywhere near it. Hunt is still an MP and has been highly vocal during the Covid crisis - I wouldn't rule him out. Nor would I rule Stewart finding a seat and coming back - although that's more of a long shot.