Our two daughters moved back in after the graduated from college. We wanted them to get a head start on paying off college loans so we told them they could move back. It took some time for daughter # 2 to find a job, but she finally did. They stayed about 2 years. Towards the end, their father was giving very big hints it was time to move on. I enjoyed having them around, (except their irrational reluctance to do the dishes! argh!), but, I too was ready for them to move on. Happily, they didn't move far. They got an apartment together about 6 miles away. Eventually, they got on each other's nerves and the younger one moved.
If anything happened, they could move back in with us. If anything happened to anyone in my family, they would be welcome - for how long would depend on the circumstances of course - that what family is for.