If I use index match to refer to column A, how can I return column B if there is a value in column B, but return column C if there is no value in column B?

This might work pre Office365 (I can't test) but may need to be array-entered (Ctrl+Shift+Enter rather than just Enter when committing the formula to the sheet):

I'm using Excel 2007.
Thanks for your tips. i notice there is one variable I forgot to mention.
G10 (my lookup) can be a value in either column A or B.
If it is a value in column B, I want to return C.
If it is a value in column A, I want to return Column B, unless Column B is empty, then I want to return Column C.