If you use Lightroom Classic and synced all your images to the Adobe Cloud, be aware that LrC only uploads Smart Previews of your original files. These SPs would therefore be pretty useless if you lost the local HD that contained your originals (and didn't have a proper backup of them). To delete all the smart previews from the cloud, login to your LrWeb account via your browser (lightroom.adobe.com, use the same Adobe ID credentials as you use for LrC), click on your avatar top right of the browser window, select Account Info from the drop-down menu, then you'll see the option to delete the Lightroom Library (all your assets stored in the cloud). But only do that if you are certain that you want to delete everything from the cloud.
If you were using the Lightroom desktop app, everything you synced to the cloud would be full original files and they should still be there.