I don't think it's really indefinitely. Sun-synchronous orbits are usually 600-800km up, and atmospheric drag makes orbits at that altitude decay eventually. It'll probably take decades before it's gone, but it's not stuck up there forever.
Another big debris incident was the 2009 collision of an Iridium satellite and a dead Russian communications satellite:
When you think about the volumes involved, it's pretty amazingly bad luck that they managed to bump into each other. These were fairly low and the debris is deorbiting reasonably rapidly, so it's not as big of a deal.
Another big debris incident was the 2009 collision of an Iridium satellite and a dead Russian communications satellite:
https://en.wikipedia.org/wiki/2009_satellite_collision
When you think about the volumes involved, it's pretty amazingly bad luck that they managed to bump into each other. These were fairly low and the debris is deorbiting reasonably rapidly, so it's not as big of a deal.