True.Washington didn't have to win battles, he just had to keep an army in the field- and even with the defeat at Saratoga (which wasn't even suffered by the main Continental Army), the Continental Army under Washington is still operational. With the POD being Clinton's army reinforces Burgoyne's army that means that Washington and the Continental Army are going to be able to go into winter quarters for 77-78, and thus get the training of Von Stueben.
If Benedict Arnold isn't dead, then he is probably in New England, organizing militia there to harass the British. New England was the originial hotbed of anti-British activity, and the political leaders there (John Hancock, John Adams, Sam Adams, etc) know that they are marked for death in the event of the British forcing the conflict to end.
So what would the next move be? I would say the British have two options:
-an attack on Philadelphia, which is the largest and most important city in the American colonies, and whose loss would keep up the feeling that all is lost;
-or a new campaign in the South, where the British believed that there were large pockets of Loyalists waiting to support the Crown.
Victory at Saratoga does not take the whole rebel army out of the field. But what it does is contribute to the feeling of hopelessness, creeping defeat and losing war of attrition on the rebel side. Lack of conspicuous conventional victories would stave off French joining the war. Only Continental Congress can surrender at a large scale, but summer soldiers can individually choose to defect, surrender, desert or retreat.
Benedict Arnold defected OTL and one of the excuses he offered was that the Brits had redressed the grievances. Now, with Arnold isolated in New England and the Brits offering terms, he might very well be able, instead of secretly attempting to deliver forts, address openly his summer soldiers and persuade them to accept British surrender terms the next time they are at a tight spot. After some political leaders in New England have been hanged, the Continental Congress in Philadelphia will debate on whether to wait for Washington to follow Arnold´s lead, or take the British terms and save their own necks and those of their remaining adherents.
Is it plausible?