Okay, these are good questions and I wish they could make a similar scenario in the third SG DVD movie, but I am not Brad Wright, so only he knows what he has planned to close this story.
We don't know how far are they. But even if it would be 300 galaxies, they could reach them within weeks or months with the gatesystem / supergate system combination. Travel in gate memory, then travel through supergates between the galaxies. So everybody could return within 1-2 years or less.