The problem with your scenarios is that, absent cheap FTL drives and a convenient habitable planet, your scenarios are insufficiently dire for evacuation to make sense.
The cost of evacuating people is the actual transport cost, plus the cost of construction of new places to live. Even if transport costs are zero, as long as Earth is more habitable than the place you're moving people, it's cheaper to just build habitats in place.
There are possible disasters on that scale, but they aren't 'ecological collapse the Earth will take decades to recover from', they're 'everything dies' scenarios. For example,
mega-asteroids (and I"m not convinced that it wouldn't be easier to deflect the impactor or just endure it even so). A
Theia scale impact would do the job, but isn't going to have anyone investigating the ruins of Earth...