Minus 30 C is the same as - 22 F. I got down to -22 F last winter and my birds still had water to drink. Any colder than that and I'm not sure what would have happened. At that temperature I noticed some frost forming on the top of the water.
My waterer is going into its 4th winter. Hasn't broken yet. I have some spare nipples in the drawer. Since my nipples are getting old I'm going to keep an eye on them this year. If I notice any getting slower I'll just replace them.
I have never heard of a chicken that would decide death was better than using a horizontal nipple. Both my neighbors on each side had chickens for a few years. My birds and theirs would all free range together. Even their chickens used the nipples at my place rather than run home for a drink. I can only tell you that I have had several batches of chickens over 5 years. I have never had a chicken that did not learn to use the nipple within a couple hours. Most were using a nipple within an hour.
No, they will not get their tongues frozen to it. They push on the metal rod with their beaks. Then they swallow the water that comes out. Other than the rod the rest of the nipple that they will touch is plastic. If the water isn't frozen i don't see how they can freeze their tongues to thawed out water.