Herceptin - How long does it work?

I have mets to the lung diagnosed in October, 2003. Thankfully taxotere and herceptin knocked them back. I am currently on herceptin and femara (also zometa for bone mets) and they seem to be working well. I have heard that femara usually works for about a year. Does anyone know if when the femara stops working and I switch to either another hormone or chemo, do they continue the herceptin or since there is disease progression do they also stop the herceptin? Just wondering if herceptin could be used with another drug once there is disease progression with the first drug. I'm so thankful that herceptin is available!!!! So far, it has been like a wonder drug for me.