Roamy here. The German X-ray observatory ROSAT will be re-entering the atmosphere as early as today, more likely tomorrow or Sunday. They expect most of the optics to survive re-entry. The mirrors are made out of Zerodur, a ceramic with nearly zero coefficient of thermal expansion, so it’s very stable in the temperature swings of space. I did some tests on gold, chromium, nickel, iridium, and platinum coatings on Zerodur substrates a very long time ago. This Sky and Telescope article mentions gold on Zerodur for ROSAT. Our X-ray telescope, the Chandra X-ray Observatory uses iridium on Zerodur. Chandra is in a 83,000 by 9,900 mile orbit, so it will be a looooong time before it re-enters.
Also falling from the sky this weekend is the Orionid meteor shower. The Earth will move through the debris left by Halley’s comet. The scientists down the road from me will be looking for meteor strikes on the Moon. So if you’re awake very early tomorrow morning, look up.