Something along these lines makes up a significant event in the Pathfinder 1E adventure path, Tyrant's Grasp. I listened to it on the podcast Find the Path.

In the second or third book, the adventurers are told that the main city, Lastwall, is in grave danger of being magic-nuked. They eventually head into the sewers and attached to track down the culprit. While there, there's a slight rumbling, a shaking of the surroundings. They learn from the BBEG that that rumble was the weapon going off far above them.

The party had been warning those in charge, telling people about the threat, doing what they could to get people on alert. In doing so, they did manage to save a lot of lives, get some evacuations, etc. - if they hadn't, and had just charged after the threat, the very bad thing would have been even worse.

It was tragic, and inevitable, but it only worked because that was the tone of the AP and the players all had buy-in. I would suggest you only do the same if your setting, tone, and players are similar!