Valentino,forget the whole 'Concorde agreement' thing. It will be on free to air unless someone offers more money, simple as.
But yes, there is a problem with the very core of this argument. BBC are looking to drop F1 to save BBC4. Seen as BBC3 and BBC4 spend half the day off air, and there are an incredible amount of repeats shown across the 4 channels even when people have iPlayer and recorder boxes, I don't see the need for both channels. Could they not cut the number of repeats, and combine BBC3 and BBC4 together into a single channel. Also, nowhere in anything I have read have I seen the viewer figures for BBC4?
However, as has been said, its nothing to do with figures, its to do with costs. F1 on BBC costs more than BBC4, so dropping F1 saves more money. Showing nothing but repeats of Top Gear would save even more money, but that doesn't mean its a good idea does it!