The general idea is pretty cool, although I don't really like some of the effects that happen as the days progress. Good examples (but not all) would be:
-higher mob spawnrates (rates are a bit too high, and should increase progressively throughout all 7 days)
-Corruption/Crimson increased spread speed and range (no...)
-Enemies spawn outside of their respective biome (why?)
-Solar Eclipse and Blood Moons fuse and happen every night (re-using events in a new event? boring!)
-Nonstop Rain (rain is just annoying and already happens too often imo)
-NPCs slowly degrade in health (why?)
-Water evaporates (again: why?)
-Lava covers up the entire map below sealevel very slowly (this would be a bit too annoying)
Instead of re-using old events here, wouldn't it make more sense to have it's own set of enemies? As the days progress they are more likely to spawn. It seems kinda like you are just throwing in random, weird and annoying things. Just because there is a black hole doesn't mean that illogical things could start to happen.
So, my conclusion is that this could work but needs a lot of work on the design side.