Sounds like you are using iCloud Photo Library (beta)?
If you visit icloud.com on a desktop browser you should be able to check to see if you're iCloud information, documents and photos have been saved properly. If they have, then they will be restored when you sign back in; though it may take a while, depending on how fast your internet connection is.
Make sure you check with the same iCloud ID that you intend to use on the iPad.
If you are not using iCloud Photo Library, then the only other photos that I can think of that would be deleted is Photo Stream. If you are using Photo Stream, be sure to copy all the photos you want to save to your Camera Roll (or elsewhere) before signing out. You should do this periodically anyway. Photo Stream is not a permanent album. It is limited to 1000 photos, after which older photos are deleted to make room for new ones.
Because it is temporary, and only meant as a convenient way to copy new photos between devices, it will not restore from iCloud.
The other photos that would be deleted from the iPad if you sign out are the iCloud Photo Sharing albums. These will also be available when you sign back in, though you may have to actually open the albums on the iPad for the photos to download.
Photos in your Camera Roll, if you still have one, will not be affected.
When you use iCloud Photo Library the Camera Roll is replaced by All Photos. Photos may or may not be stored at fill size on the iPad in iCloud Photo Library, depending on you other Photo settings. This makes it hard to predict what might get deleted when you sign out of iCloud.
One last note. With iCloud Photo Library there is some risk. It is still in beta, so it's always possible it will burp and cause unexpected problems. Or more accurately, it's somewhat more likely to have problems than the older, stabler, photo library features.