Ryuuko's probably getting it back next episode anyway...
Or maybe they'll do a REALLY dumb asspull and say, "LOL Nui you only have the Fake Scissor Blade! Why do you think Senketsu isn't permanently dead this whole time after cutting him up in episode 13, or cutting him up last episode," and then Satsuki will pull out the Blue Scissor Blade and go keikaku, Mary Sue, Satsuki a best etc. and she'll give Ryuuko the real Red Scissor Blade as they had made up a fake while she was in her angst-coma. And then Senketsu will go "I was Isshin the whole time," and everyone will start laughing about Nui got outrused etc.
Ok so I think I got carried away with that last part but basically I don't believe Nui will have the full set of Scissor Blades for that long
Trigger must do an entire series of hilarious outtakes on the final BD!
That compromising scene with Ryuko backwards and the COVERS ganging up on her