My MacBook recently died and I lost my Lightroom catalog (was not backed up anywhere aside from internally). However, I can still access this lost catalog and its associated collections / edits from my Lightroom Mobile and web accounts. My question is: is there any way that I can restore these collections and edits to my new catalog on my new computer?
You must have a working backup catalog to be able to recover the lost data. At this point, the moment you will create a new catalog and start syncing it, the data stored online will be replaced with the new synced data.