SWEPT and HIGHLY TAPERED flying wings can get away with it because the sweep and taper puts the center of drag behind the center of gravity. The old Klingberg wing and the Northrop bombers are expamples of this. However it's a touchy thing. The Klingbergs were well known for acting like they had a hinge in the middle and would oscillate in yaw under various circumstances. The Northrop bombers used the "fin" effect of the prop discs and propellor extension housings to provide the vertical fin effect. Note how when they went to the jet design they had to add little fins to compensate for the missing props and housings.

So it's not correct to say you do not NEED a vertical stabilizer. You DO but there are some options depending on your planform.

For conventional models you can't get away without one. It has to be there or the model just will not fly for more than a brief and exciting show of nutiness. However I fully agree that you do not need to use a rudder. But if you do not have one forget about ground based takeoffs and switch to handlaunching. The only way you can take off the ground without a rudder safely and predictably in varying wind directions is with a rudder. Ailerons are not usable until the wheels leave the ground. I know a few deltas and others have used nose wheel steering via coupling to the ailerons but I'll bet there are some anxious moments during sidewind takeoffs.