It takes a few centuries for anything with less than a 1000km high orbit to have decayed and returned to earth.
Assuming that the previous civilisation was many thousands of years ago everything will have burnt up on reentry, crashed into the sea, or been destroyed by the Alien technology that got rid of the last civilisation.
Assuming that the previous civilisation was many thousands of years ago everything will have burnt up on reentry, crashed into the sea, or been destroyed by the Alien technology that got rid of the last civilisation.