Deleted all partitions on Fusion Drive. Don't know how to recover
Could you manually erase the drives via terminal, then recreate a fusion drive.

To manually erase the drives, go into terminal and do diskutil cs list. Then you'll need to do diskutil cs delete (lvgUUID). Here's more details: http://www.macworld.com/article/2015664/storage-flash/how-to-split-up-a-fusion-drive.html

After you delete it, you can recreate it: http://www.macworld.com/article/2014011/how-to-make-your-own-fusion-drive.html