If Sunak had resigned when a lot of this stuff started, feel like he'd have a shot at being PM now. As it is, can barely see him in politics much longer. If you bin the work you're doing where you're earning megabucks I think the aim is probably to get the PM job... not sure he'll ever get close now (what a shame).
Like
@hulloutpost says, improbable that it brings down Johnson. Even the e-mail newsletters etc this morning focused on Sunak rather than the PM, and it seems like Sunak's rule breaking was less egregious. Perhaps if it were not for Ukraine and the ensuing media landscape the heat would be turned up a bit more on him too.
Tbh, Sunak hasn't seemed very good at politics. Rumours are that he'll get fired soon anyway after the spring statement and falling out of line with no.10 - you'd think if he had resigned even yesterday, the heat would be on Johnson (at least a little bit)!