I think her powers would of advanced further like we seen in some of the episodes like Primrose Empath and got new powers that related to her other powers.
I think Andy would of been able to come back at the end of season 8 so then it would show what they did in the years after that.
I think Prue would of still done things for her sisters, but also starting a family with Andy.
Some of that what I thought of I have thought of before having my own Charmed fanfic and all where Andy is mentioned in some of them as in my Charmed fanfic Prue is still alive. So its the power of 4 instead.