Soyuz Backup Periscope (ВСК-4) is used in Soyuz spacecraft to align itself for orbital corrections, deorbit burn, and rendezvous with the International Space Station. Here is a cute closeup photograph of one such unit:
NASA's poultrynaut Camilla looks through the Soyuz Backup Periscope (ВСК-4) used to align the Soyuz spacecraft. (Image: SDO)
Most of the time the view of interest is the one "straight out" along the axis of the periscope. Whenever there is a need to fire the engines, the reference orientation in which the Soyuz puts itself is along the local vertical: in this orientation the periscope faces towards Earth. The optical setup is such that the commander sitting in the center seat will see the entire globe symmetrically in the field of view if the Soyuz is properly oriented. Also, any feature on the surface of the Earth will be running from top to bottom (or from bottom to top if it's a braking attitude).
When we approach the Station for rendez-vous the mirror is turned so that the commander can now have a forward view. This is the view we would use to align the Soyuz manually if we had to fly a manual docking.
Quote and photograph source: Samantha Cristoforetti on Google+, image credit: NASA
But this periscope is a part of the landing module (the middle section of the Soyuz vehicle) and the periscope doesn't seem to retract into the module at all, so...
Is this Soyuz Backup Periscope (ВСК-4) disposed of after the deorbit burn and before the atmospheric reentry, when the crew landing module separates from utility and instrument-assembly modules of the Soyuz spacecraft, and if it is, how is the remaining gap in the landing module's external hull sealed / secured to thermally insulate the capsule for the reentry?