I'm a little fuzzy on the POD: if de Grasse is caught by Rodney, then the biggest difference is that he can't send his transports to Washington in early September. However, Washington had been march toward Virginia since August 19 or so; by the time he de Grasse sent his transports, he was in Philly at least. Additionally, Wiki says that Washington visited Mt. Vernon on the way to Yorktown. I'm not sure if he did so by sea or by land; if the former, then we can conclude that the march to Yorktown may be delayed, but not thwarted. If the latter, then Washington should arrive on schedule, simply without de Grasse's 3,200 men and without much support from the French.
If the seige is delayed, Cornwallis may attempt to fight Wayne's forces before Washington arrives, but that would be a big gamble. He may prefer to wait for Clinton to send reinforcements from New York and thus allow a seige to begin. Either way, I don't really see what it means for there to be "no Yorktown" under such circumstances. There's going to be a battle of some sort.
Now, I think what the OP means is that the ATL battle lacks the finality of Cornwallis' surrendur, which leads to a mediated peace. I'm not sure Spain and France would go for this, since IIRC they still haven't failed to take Gibraltar or Carribean islands. Both of these nations are in the war to bloody Britain's nose and they haven't really had their chance in 1781. It's possible, then, that Britain is forced to concentrate both on manning troops in the USA and fighting off the Spanish and the French from 1781 onwards, which may well prove harder than OTL.
Furthermore, Russia will hardly be a neutral arbiter and will be disposed to give the US a good deal so as to give the British a bad one. Also, how exactly does Russia benefit from stopping the war? It's not as if they can force the British to terms and they don't benefit from France and Britain exhausting each other. Hence, presuming a peace under Russian auspices may result in a peace with the same borders as OTL, but with far different circumstances on the ground: more chaos in the USA, perhaps more trouble with freed slaves (which might be a long term boon). It might also result in the British retaining some land from GA to Ohio, but it might also not.