Eventually you will be able to put them back together but it can take a long time. Several months is common for my kids, and they will often still try when I put them back together. I think it took 4 months for one of my doelings before I could put her back with her mom, as long as she had been nursing on her mom! But now they live together fine.Yes you will have to separate and can't put them back together.
Some does do wean their own kids (none of mine ever have, lol, but I have heard this from other people), but usually that is sooner than 7 months, at this point to get her weaned you will need to get them apart.