Devs does close the sectors which are completely empty or almost empty. If you look at shards stats, you can clearly see that shard0 is currently underpopulated comparing to other shards.
As for your blocking expansion, well, they specifically made it so players won't lost their connectivity to the remaining world. I mean portals that surround closed sectors, they lead to the opposite side of the sector, and they're free of ttl penalty (they work as central portals). You can use them to access sectors behind closed ones.