You can still warp out with a memory disk, and the stop sign isn't necessary-- you can just land on the edge (you almost certainly don't need to be a mouse either,but that's a lot harder, to the point where I'm not 100% sure it's possible). I think the end sign also may let you out, but I haven't tested it yet just in case. Hopefully there's a dialog option with Silica where she notices the softlock and fixes it for you if you show her the disks with no other disks or something.