Removing bathroom tile from cement backerboard
If the backer board is attached with screws, the easiest solution would be to find them, remove them and take the floor out in chunks. However, that's not gonna happen since there isn't a good way to find the screws and you'd have to chip up the tile to get at them. 

I removed almost 600 sqft with a rotary hammer from Harbor Freight. I bought the mid-range sds model. I don't usually buy power tools form HF, but this is one that you will probably destroy during the process, so buy accordingly. I went through two of them (replaced under warranty) to finish the job.

Regarding the cement board. You won't know for sure that you have to replace it until you get the tile off and it cleaned up. depending on how much you beat it up and how much grout and mortar is left, it may be easier to replace it. You may need to pull it to level the floor anyway, you just don't have enough information to make that decision yet. Good Luck! Oh and get good knee pads, they are a life saver when chipping up tile.