Today’s Question: What happens if your Lightroom [Classic CC] catalog gets corrupted and you have web albums synced via collections? Will the web albums stay intact forever?
Tim’s Quick Answer: If your Lightroom Classic CC catalog gets corrupted, your synchronized collections will remain available via the cloud until you create a new catalog and designate that as the catalog to be used for synchronization. Therefore, in general it would be better to recover from a backup catalog than to create a new catalog.
More Detail: When you enable synchronization for collections within Lightroom Classic CC, the images within those collections will be synchronized to Adobe’s Creative Cloud servers. That, in turn, will cause those photos to be available in the Lightroom CC mobile app, via the Lightroom web interface (https://lightroom.adobe.com), or via Lightroom CC (the cloud-based Lightroom).
If your catalog becomes corrupted, that won’t immediately cause the synchronized images to be lost. In theory you could access the synchronized photos indefinitely through the options outlined above.
However, at some point you would likely want to create a new catalog and enable that catalog to be used for cloud-based synchronization. Because only one Lightroom catalog can have synchronization enabled, as soon as you enable that synchronization for the new catalog your cloud-based storage would be updated to only include photos (via collections) that are being synchronized from your new catalog. As part of that process, the photos that had been synchronized to the cloud will be removed.
Because of this issue, if your Lightroom catalog becomes corrupted, it would generally be better to recover from a recent backup of your catalog, rather than creating a completely new catalog.