Not sure. There's always the campaigns of the next year - the army that Burgoyne lead OTL.
Note, the following is posted as someone with a low opinion of Howe - the human element that may or may not break a perfectly good plan.
Howe had enough men to hold New Jersey OTL - Raul's force at Trenton for instance is nearly as large as the force Washington managed to attack it with (1,600 vs. 2,400 I believe). I do not doubt that the arrival of more men would help if he cares to use them vigorously, but that's in doubt.
Come spring, given how badly Howe handled the beginning of that campaign, and how irrelevant reinforcing Burgoyne was to his plans . . .
Also, a minor note and a question:
Note: Accodring to this,://militaryhistory.about.com/od/americanrevolution/p/American-Revolution-Battle-Of-Brandywine.htm Howe had 15,500 men at Brandywine OTL.
Question: Where is your source for the number of men in Newport and (implied) New York?
I'm not arguing with it, as I don't have a figure myself handy, just curious as the American Revolution has at times been one of my interests in terms of military history.
Howe was a decent tactician; he never lost a battle in that war. He also learned from his mistakes; after Bunker Hill he eschewed frontal attacks. As a strategist he came up short, failing to recognize that attacking Philadelphia would preclude supporting Burgoyne with an advance up the Hudson, for one example. As a subordinate general he would have been a fine commander, but as a commander-in-chief he was not up to the task.
Clinton had occupied Rhode Island in December 1776 with an original force of 9,000 men. Allowing for wastage there should be roughly 8,000 there in the spring of 1777, although that number is my estimate in this case.
Howe's original force in August 1776 numbered 32,000; this includes the troops later sent to Rhode Island. Assuming normal wastage (battle casualties were minimal) he would have 22,000 or so in the spring of 1777, again my estimate. He took 16,000 to Philadelphia, which accords well with your figure, leaving 6,000 or so to hold New York and cooperate with Burgoyne, which is clearly inadequate.
If we add to his force 18,000 Russians this gives him 40,000 in New York plus 8,000 in Rhode Island. If he sends 10,000 up the Hudson with Clinton to cooperate with Burgoyne and takes 20,000 to Philadelphia himself that still leaves 10,000 to hold New York, which should suffice.
By the time the Russians are being shipped from England (July/August 1776) the Rebels have been chased out of Canada and Carleton is poised to advance down the lakes toward Albany. Benedict Arnold's makeshift fleet managed to delay that until October, by which time it was too late to advance, but Burgoyne is ready to advance with 7,000 in the spring while St. Leger advances from the west with 2,000 at the same time. This is all OTL, BTW. The need for the Russians there is slight; furthermore they will be more useful with Howe and the difficulty of supplying them there will be lessened.
Add to Burgoyne's and St. Leger's forces 10,000 more coming up the Hudson and the Rebels are clearly going to have to scramble to hold Albany and preserve their communications with New England. The coming campaigns should be quite interesting. Does Washington abandon Philadelphia to hold Albany? Or does he trust Gates and Arnold to deal with the threats, perhaps sending them additional forces?