In iBooks on the iPad go to Store, in there tap on the Purchased button at bottom of page to see a list of all purchased ebooks.
If you have too many then tap the "Not on this iPad" tab at top of page to see only those purchased ebooks not currently installed on this iPad. Find the missing book, it should have the iCloud icon next to it with an downwards pointing arrow, tap that to redownload the missing ebook.
No it shouldn't. Just deleteing a book from your iPad should leave it available for download from iTunes again in the future. Once you've bought the book it's yours to download onto as many iOS devices as you like.
Are you sure the book isn't listed under Purchased in iBooks Store? Did you do a search for it? Tap the "All" tab and then type title of book (or part thereof) in the search box at top right of the screen and Search. If you have purchased the book then it should show up in the search results, with the iCloud download icon rather than the price button you get for books in the store you haven't purchased (why it doesn't limit the search to just the titles you have already purchased given that you're in the Purchased section I don't know, but that's the way it works unfortunately.)
Boy I'm almost too embarrassed to admit this I must have been having a blonde moment (lol) I found the book I was looking for, however it was in my Kobo App. But I have a good explanation though? Want to hear it? Ok, so I bought Gone With the Wind through the iBook store so I just assumed it's sequel “ Scarlett ” would be in my iBook library but we all know what happens when we assume things. But on the bright side of things if I ever lose a book in iBooks at least I will know what steps to take to retrieve it ☺️.
Thank you for all your help David!