You explained it nicely.
My experience with Photo Stream on a computer is limited to using it with Aperture on a Mac. As long as you fire Aperture up and let it sync your Photo Stream, it stays permanently in Aperture. If something was deleted from the stream before Aperture was run, it never showed up. Or so it seemed the few times I used it.
Apple specifically said that Photo Steam does not automatically delete from the Mac, but that does leave room for some quibbling on whether deliberate deletions happen, or if the PC might act differently.
We are also in a time of change, withApple revamping how it handles photos in iCloud and all it's apps. That makes it hard to tell exactly what might or might not work right now.
You're best, safest bet is to manually save those photos off the iPad.
Here are a few options; with some guess works since I no longer have an iOS 7 device to play with.
You can select and save them to Flickr, or FaceBook from in the app. (if you have those apps installed)
I'm fairly sure you can use the Google Drive app to save photos from the Photo Stream. DropBox might work now. I'm not sure. Not long ago it would only access the Camera Roll. Other cloud app/services might work as well.
My favorite photo transfer app is
PhotoSync. There is a free companion app for the PC and Mac that makes it even easier, but it's not strictly necessary. As a bonus this app is also available on Android, making it one of the few easy ways to move pictures between non iOS devices. This is probably your best bet for bulk transfers.
There are other methods, but these are the ones I'm most likely to use.
Good luck.