This is hardly without precedent - the old 50P was demonetised as recently as 1998. The world appears to have coped. (And "Billions" - Wikipedia claims there's

This is hardly without precedent - the old 50P was demonetised as recently as 1998. The world appears to have coped. (And "Billions" - Wikipedia claims there's an estimated ~1.5 billion pound coins in total circulation. The overwhelming majority of those are going to be exchanged during the changeover period, and even after that banks will tend to accept them for a significant amount of time. There's no way that the amount of money written off is going to be anywhere near that)