A player is handing you a campaign-spanning objective loaded with adventure seeds
I’m failing to see the problem.
The player needs to:
- Find out what the clouds actually are
- Why they are there
- How they can be stopped
- Gather the required materials
- Overcome the people who don’t want home to succeed because reasons
- Find out the unintended consequences of succeeeding
- Deal with those
If there aren’t 2 dozen adventures in that you aren’t trying.
Of course, this can be a secondary story with clues scattered through the main thrust of your campaign. Or even one or a few side adventures so that everywhere he goes everyone wants to met the guy who beat the clouds.