Well, I prefer to think that if the cermony hadn't been interrupted they would have thought about digging her up, like this:
"If the spell worked, why isn't she here?" asked Xander, confused.
"I don't know! It finished! It should have worked!" replied Willow. She was baffled.
"Oh dear god." Xander said, blanching as a thought crossed his mind. "you don't think she's...down there? Alive?"
Willow felt faint. "I - I - oh god! Oh god! The shovels! Are they..."
Anya was out of the clearing, running to Xander's car. "In Xander's trunk! I'll get them!"
"Hurry!" cried Tara, as she joined Willow and Xander tearing away the loose sod that covered the grave.
They imagined they heard a pounding deep inside the earth. Or was it imagination? Xander stood up and found a dead branch on a nearby tree. It yielded quickly to his powerful grip. Even as his mind was on Buffy he felt thankful for the strength given to him working construction during the past year.
Seeing that they had started digging by hand, Xander told Tara and Willow to stand back. He plunged the large jagged end of the four inch branch into the soft earth near the headstone and began dragging back the dirt.
Again and again he dug, taking chunks of earth out of the ground, flinging it every which way, making some progress. By the time Anya returned with the two shovels, The adreneline was coursing through his body and sweat was dripping out of his shirt sleeves.
Whipping off his shirt, Xander wiped off his brow and chest, and grabbed one of the shovels. Anya stared for a second at Xander's intensity and started in at the foot of the grave.
Tara consoled Willow, who was starting to fall apart. "My fault," she cried, "it's all my fault. I should have known."
"Shhh," conforted Tara, "We all should have thought of it. You missed it. I missed it. We all did."
In the distance, the sound of motorcycles grew closer.
Xander kept digging.