Hallo Kaethe Ko,
The previews folder can grow quite big without any problems.
Mine is ca. 115 GB, for a catalog of 113'000 images and 1.6 GB size of the lrcat-file.
That works pretty fine.
So you might have had a corruption problem. Of course this should not happen. For such catalog-preview-sizes it would be really inconvenient, as recreation by LR would take a week running in the background.
Hopefully your overall catalog size was not that big that the previews-recreation will take so long.
Cornelia