We saw a little of what Prue might have been in the future in 'Morality Bites'.
I think her powers would definately have grown to that kind of strength and Astral-Prue would have developed a telekenetik ability too.
I agree that Prue would still be working but she wouldn't be a total workaholic like she was in 'Morality Bites', she would have a much more balanced life and always put her family first.
I'm sure that she would have a long-term boyfriend but I'm not sure she would be married and I don't think Prue was really the maternal type, so no kids (but she would help look after Piper's and be really protective of them).
Having said all that and as much as I'd have liked to see Prue carry on, I'm glad Shannen got out when she did. It was the right time for her to leave and she's gone on to better things. The plot lines in the later seasons got weaker and very silly, Shannen would have hated that and she's far too talented for that sort of work.
Prue was the best but only because Shannen is an amazing actress.