Could I have enough chain retention on a 1X system with just a narrow wide chainring without a clutch?
It depends on the terrain you are riding. If you have lots of rocks on your trails, like in Mediterranean countries your chain will fall here and there. On the other hand, if your riding terrain similar to nice flowing Alps singletracks, having narrow-wide chainring will probably be enough.
Also consider installing a chain guide, it costs about 10$, weights little and can save your chain from falling quite a lot. And don't forget a beefy chainstay guard, otherwise the sound of chain hitting alloy can drive you mad :-)