Extension Of IFERROR / VLOOKUP Formula?

look at the tab "Publisher sumif summary" and at the "Q" column. There is already a formula in place which returns a number from column B in the "Publisher Control Sheet".

If you look at Column B in the "publisher control sheet", you can see that for some of the companies in column A there is no number. Instead, there is a number in Column C where there is no number for column B.

The problem at the moment is that I don't know how to get the data from Column C factored into the equation, which I will describe below

Essentially, i need the formula in the Q column of the "Publisher sumif summary" to return "((Column M number (impressions) /1000)* Column C number) with the column C number coming from the "Publisher control sheet" tab. It needs to only do this where there is no number in column B, and how to add this function!