I know this going to be a long one but an AU where Dan and Amy never broke up the first time- they however did almost break up or temporarily broke up multiple times but never for long
Normally I hold onto prompts until such time as I think I’ll get round to writing them, but in this case I’m going to answer immediately.
Because there’s no way I could write this and have it be in character and not simultaneously INCREDIBLY depressing. The only reason Dan would maintain a relationship with Amy for all that time is if he thought it would benefit him professionally.
Dan is extremely transactional about relationships – if they don’t clearly and obviously benefit him, he has no interest in them. It has taken years, literally, for the show to develop him to the point where he appears to value his relationship with Amy as a relationship – where the pleasure of her company and her physical presence outweighs (or at least) equals other considerations. In fact, we don’t even know that he’s reached that point yet, it’s just implied by his actions.
So for Dan to have reached that point two or three years before the show (so, roughly eight or nine years earlier than he has in canon) would require such a substantial change in his development that I don’t think I could write it and have it make any sense. Maturity takes time, and Dan still needs some of that.
That said, if someone else wanted to take it on, and have fun with it, I would encourage them. It would be a fun, and long, project.