My absolute nr.1 rule is: Keep sleeping bag dry.
Rule nr.2: If sleeping bag is wet, dry sleeping bag out.
Sometimes it is just not possible to keep sleeping bag dry, which is a reason I use synthetic bags. Bulky, heavy, but when wet far better than down.
I have slept in wet sleeping bags. Not fun at all, but better than no sleeping bag.
I pack my sleeping bag in a big black trash bag inside an Ortlieb pannier. The trash bag kan be slept in, pulled up over wet sleeping bag for extra warmth.
With a good tent and diligence sleeping bag can be kept dry almost always. The ”almost” is important though, and may well be a survival situation.