With next update, cuffs and gags will no longer detach when the HUD is not worn.
Instead, the cuffs and gags will simply not be operable (can’t click on them, give commands, lock/unlock) till the HUD is worn.
If the sub is locked, detaching the HUD will still incur a breach (non-RLV users of course).
Also, SL has an intermittent bug that detaches HUDs (not just the LULU one) on login. Now the cuffs/gag will tell you that it can’t find the HUD and give you some time to re-wear. If you don’t re-wear within the time frame (it will nag you, don’t worry), then it will trigger a breach (triggering alarms and ending Trials, if applicable).
In all events, so long as the HUD is not worn, the cuffs/gags cannot be operated on.