It depends. There are many types of metastatic breast cancer. Life expectancy depends on the type and the location. Er+ breast cancer that has spread only to bones has a life expectancy of years, even 5-10 years. Er- breast cancer has a much shorter life expectancy. In general, breast cancer in organs (lung, liver, brain) causes death sooner than breast cancer in bones only. Ask your oncologist.
It varies. In general, less than 20% of women diagnosed with metastatic breast cancer will be alive 5 years after their diagnosis. However, this statistic may vary quite a bit depending on which organs the cancer has spread to and which drugs the cancer may be sensitive to.