I had not realized that you intended this to be the story's final chapter until I looked at the story's summary to see if a new chapter had come in today, and I saw that you had it marked as "completed". Wow, what a surprise.
It is a minor resolution, and it's certainly your prerogative as an author to end it where you think best. One of the issues it leaves open for me is what the Weasleys will do with their idle capital now. I have a difficult time imagining George and Fred letting Death Eaters initimate them away from opening a similar Muggle shop. Yet the fact that your narrator writes "Fred and George wanted to
stay well clear of the muggle world." implies that this is what happened.
Another loose end is why Harry didn't cash the Muggle check for them, given that he's an investor.
I've used my rating points to positively rate several chapters of this story -- I think I gave you an "ambiance", an "original", a "funny", and an "exciting", all from me. However, because of these issues, I'm going to have to add a negative rating as well for this chapter; I'll use "OOC".
Author's response
I'm glad you liked the story. Sorry there isn't more but I ran low on ideas and started getting busy with other things. I's leave the major resolutions to the incomparable J. K. Rowling.
As far as Fred and George are concerned, I agree that a few Death Eaters wouldn't scare them but a triple threat of Death Eaters, muggle gangsters and a muggle insurance company were just too much.
I'll correct some of the typos you pointed out.