1 hour after people: The OrbeTower consumes so much power that it's power fails, but it takes 2 hours for the last light to fail.
1 year after people: Plants climb the bottom floors, but only to a height of 5 km, a small fraction of it's total height. At 5 km, no plant can grow because of low air pressure.
10 years after people: The glass up to the 500th floor breaks, as 10 years proves too much for the glass without being clean.
50 years after people: Debris and small meteorites threatens this OrbeTower, the 150th highest floor up have collapsed, causing a chain reaction.
500 years after people: The top section has collapsed, threatening more chain reactions.
'15,000 years after people': OrbeTower has slowly collapsed over neglect by the dust and micrometeorites beyond 10 km, and rust below that. The space is now unrecognizable. However, the metal mixture will stay for billions of years.