I assume this deprication will probably be cost related but I am curious about the implications on the emergency side of things.
With VoIP, you tend to have your own, plugged-in wall box. Which becomes useless the moment your electricity stops, e.g. in case of natural disasters.
Also, analog telephony just sounds better than digital one. No downsampling happening.
Also, all phone lines these days, wether POTS or VOIP are digitally trunked and switched.
Some spare parts have been out of production for decades. If one of those parts needs replacement, then keeping an exchange running may now need replacing much more than just the broken part, or the technicians may try using parts from other exchanges (the number of landlines is much lower than at peak, so there are spare spares in many exchanges, so to speak). That's an expensive way to maintain a network, obviously.
VoIP infrastructure is more fragile than copper assuming equal hardware age and comparable maintenance regimes, but I assume that the lack of spare parts changes that.