First, try restarting your iPad, and opening Pages again (with an internet connection). Give it a while and see if the document re-appears.
You can also to icloud.com in a computer browser (not on the iPad). If your document is there it will be under iWorks, the Pages tab. You can download the document from there and email it back to yourself to open on the iPad.
I don't trust iCloud to keep my documents safe, not the important ones. It is simply too fast to update any changes you make, including deleting a document. Plus, I once lost all my content. Because I maintain backups on my computer, I was able to restore them. I have a Mac, and sync my iWorks documents with the OS X versions of the apps.
If you have AppleCare or AppleCare +, you have free Apple Tech Support. It may be worth contacting them and asking if they can restore the your documents from one of their backups. They might have to restore your entire iCloud account. No idea if they can, but it is worth a try. I was working with Apple Tech Support when my afford mentioned loss of documents occurred. The tech said they could restore my documents, but that it would take up to 24 hours. He could not do it himself, but had to put in a request. So there is reason to believe it's possible.
Of course, if it is important enough you can use tech support without AppleCare. You'll be charged. I don't know how much.
Good luck.
In addition to my computer backups, I use Box.com to back up the stuff I worry about. It supports WebDAV, making this a fairly painless process, though you can also choose to Open In the Box app to save documents. Note, I use this as a backup, not my working files. I just do a quick save to Box whenever I make significant changes. It takes about 15 seconds.
You could use DropBox for this as well, though without WebDAV it's slightly less convenient.
