That woman was the strongest bit of glue holding the British monarchy together. She was able to keep her position and avoid abolition partly because her reign dates back to a time when reverence for the crown was more or less a given. That she ascended right before the Suez Crisis (the incident which made it clear Britain was no longer a superpower) made her a symbol of a previously great Britain and therefore of collective nostalgia.
She was easy PR for the Royal Family, but none of her descendents have that aura that she had, and despite the best efforts of The Daily Express none of them will ever possess the level of gravitas needed to keep a monarchical system in place in the 21st century. We're about to get weeks of diamond-studded, gold-draped mourning of an old woman while we approach a winter which will see many, many more freeze or starve to death penniless.
She'll be the last meaningful British monarch. Thank god.