You have to wonder what would have happened if Yahoo had bought Google back in 1999. Would Yahoo have had the success Google has had in the last decade? Would we ever have had access to the powerful web tools that Google is providing us with right now? And ore importantly would any other company have managed to transform the Web like Google has? One thing's for sure though - Yahoo and Microsoft would not be scratching their heads over how to stay afloat and compete in this market.
I think other companies would have appeared to fill the void, it just would have taken longer.