No, the entire pad wasn’t gone. The concrete under the pad had a big hole in it, but most of the structure was intact - as evidenced by the fact that they just patched the hole and continued using the pad without having to replace the whole thing.

Nobody was hurt. The rocket was damaged, but it still managed to accomplish much of what they’d wanted it to accomplish. It was a test launch, they knew it wasn’t going to cruise all the way to the finish line. They wanted to see what went wrong.

Do you really think they didn’t do the math at all? They did the math, they figured they could risk it based on what the math told them, they turned out to be wrong in hindsight. Plenty of things seem like good risks that turn out to be bad ones in hindsight. They’re not a bunch of yee-haw wild men who do stuff without thinking or calculating, the FAA would never be giving them launch licenses if they were.