Then that would be the only possible solution: long-term terraforming.

The very idea of terraforming sounds like it would take many centuries at a minimum, but by the time we’ve reached such planets, hopefully we’ll have developed, say, AI and self-replicating machine tech to the point where terraforming might take ‘only’ generations, or even decades.

I know that sounds hopelessly unrealistic, but I think it can be done.