How many people were killed in the earthquake after the two witnesses went up to heaven?

Answer: Seven thousand

In that hour a great earthquake struck; a tenth of the city collapsed and seven thousand were killed.

“And the witnesses heard a loud voice from heaven saying, “Come up here.” And they went up to heaven in a cloud as their enemies watched them. And in that hour there was a great earthquake, and a tenth of the city collapsed. Seven thousand were killed in the quake, and the rest were terrified and gave glory to the God of heaven.”— Revelation 11:12-13 (BSB)