Someone once claimed that if Tarleton overpowered and the British Legion won, the British plan might work. I described it here.
http://www.alternatehistory.com/forum/threads/wi-british-legion-won-1781.421102/
Now the historian behind my speculation claimed that if the British Legion won, USA would just be Philadelphia, New England, and New York except the city (think Singapore).
The thing is, I pointed out in that post that perhaps Tarleton's success wouldn't make that much of a difference. He seemed liked a hot headed commander who would fall for a trap anyways. Or just bite his unit's teeth on some fort. And even avoiding all that, if he went according to plan, he wouldn't find anything suspicious about losing contact with the boss since that would be expected. So, he might end up doing nothing useful. Granted, the other guy is a historian and I'm not, but sometimes they get this wrong. At least one American historian claimed an American midway disaster would lead to the loss of Midway Island... except that the defenders outnumbered the Japanese there and a host a zillion reasons why the odds of them taking it would be below 40% to say the least.
However, there is a middle ground. Whoever partnered up with Crawley does history for living, so he might have seen something that he didn't think was important to put in his limited space, so give him the benefit of doubt. Maybe Tarleton can't save his boss if the British Legion won at Cowpens, but he can still go around seizing rebel nests. Maybe when the peace treaty comes, the Americans give up the UP since the miltiary situation, while favorable to the Patriots, isn't completely gone to the rebels. The rebels really only want the 13 colonies and the Ohio river valley (read: Indian land) anyways. Under this situation an interesting side effect is that the British might be able to force the Patriots to honor all debts the Patriots had to Loyalists and compensate property seizures. The American government will have extra debt (because the population is poorer I assume the tax base shrink) but don't worry a lot of it is French so when the French revolution comes, they can just default and give revolutionary France the middle finger, so America won't be that much worse off in the long run finances wise.
Now, the Jay Treaty is an interesting one. At around this time, America doesn't really care for that piece of land yet either. The problem is that the British don't really feel like having it either. I don't think they really have extensive settlements in Michigan. Perhaps to save face, America can claim "yeah we were too broke to pay off compensation to loyalists, but this land is worth exactly that amount." Around this time the former British colony and its motherland were actually warming up. If America was slightly more butt-kissing, they might give the region or sell it for a steep discount.