China's first space station ceased functioning. Unlike Salyut 1, Tiangong-1 has no remaining fuel to perform a controlled burn to drop it safely over the ocean. China is quite secretive about details of its space program, but according to a forecast generated by researchers at The Aerospace Corporation, it will crash back to Earth in late January 2018, give or take a month.
It's unlikely to crash on a populated area. Over 70 percent of our planet's surface is covered with oceans, and a significant fraction of the land consists of uninhabited areas like deserts. Skylab also had no fuel for an aimed re-entry, but calculations of its orbital parameters were well known and announced worldwide. Although the craft was expected to come down safely over the Pacific Ocean, the San Francisco Chronicle newspaper offered to give $200,000 to any subscriber who suffered damage or injury from its return.
Despite all the stuff in orbit eventually falling back to Earth, the only person known to have been struck by space debris, Lottie Williams, lives in Tulsa. Early one January morning in 1997, she and two friends took a 3:30 a.m. walk in the park. They saw what they thought was a bright shooting star streaking through the night sky. Thirty minutes later, Williams felt as if someone touched her on her shoulder. She looked behind her and found something that resembled lightweight metallic mesh. After sending it to various laboratories, she discovered that the material was part of the fuel tank of a Delta II rocket that launched a U.S. Air Force satellite in 1996. So chances are quite slim you will be struck by any returning pieces of Tiangong-1.
Tiangong-1 is not tumbling. That's not good. Rapidly flipping craft that re-enter tend to fall apart due to the forces on them, and the smaller pieces are quite likely to burn up tens of miles high in the atmosphere. And that leads to a different problem. The Aerospace Corporation's Tiangong-1 FAQ stated. "Potentially, there may be a highly toxic and corrosive substance called hydrazine (used to control the ships orientation in space) on board the spacecraft that could (therefore) survive re-entry. For your safety, do not touch any debris you may find on the ground nor inhale vapors it may emit."