Personally, the well being distroyed brings up a time paradox of sorts. Think about it (and be warned, I’m digging deep in time paradox theories here).
The well can only be distroyed in the future (present), because it cannot change the past if destroyed after the fact (so to speak).
If the well was distroyed in the past, it must be rebuilt again before Kagome's first journey down the well.
If not then she would never be able to be pulled through the well by Mistress Centipede the first time. Then all her adventures in the well would have never happened as time would have to reset itself to correct the time flow/stream.
If the well is distroyed, and Kagome still finds herself in the past and with memories of traveling down the well then the well must be fixed at some point in the 500 years (give or take) between then and her first trip.
Something else that could happen is that if the well gets destroyed (and stays destroyed ) and Kagome remains in the past, her memories would change to show a different method of getting to the past. For instance, there may be a hole in the base of the God Tree, etc. Whatever the method of transport, if she has her memories and still remains (with the well permanently destroyed), then time must keep itself on course and create a new passage to get Kagome there. This will show with new memories of her travels between past and present.
With time travel, everything effects everything else. You may totally screw up your timeline or it may actually be the path that time must follow to end where your present currently is. That is the danger with time travel, not knowing what could change things.
Of course, that isn’t even scraping the surface of possibilities of multiple universes that could branch off from the well being destroyed. The possibilities are endless.
But to put it simply:
If the well is destroyed and never fixed before Kagome is born, then -
She never travels back in time
She never meets Inuyasha
She would not meet Sesshoumaru
There is no reason for an anime or manga to show her adventures in the Feudal Era with Inuyasha
Without the anime and manga, or Kagome and Sesshoumaru, there would be no fan base for the show
And thusly, there would be no Dokuga
And finally, we would not be here, in this forum, reading this thread.
Sad to think about, isn’t it. It would, in essence, affect us.
And it’s all because of time paradoxes and a simple wooden well.