I can answer the first part, since the second is really speculation anyway. Okay, so, the first deciding factor that contributed to British lose in the American Revolution? Well, wars were changing in the world. No longer could leaders wage war or pass laws without expecting some sort of rebuttal, from their citizenry, nobles, or in the case of Britain, their parliament. A good bit of Parliamentarians in the British Parliament were sympathetic to the American cause (note that this doesn't mean they fully supported American independence, but supported their ideals of liberty), most notably Thomas Paine, writer of Common Sense, and Edmund Burke. Throughout the War, large arguments would break out between Whigs (pro-Americans/pro-Parliamentarians) and Tories (pro-Monarchy). This type of domestic dissent cannot go ignored or unnoticed. Now take this and add on the costs of the War on the government and Crown, which was already facing a failing East India Company (this was part of the reason for the British trying to force taxes on the Americans), and a large debt owed after the Seven Years' War (French and Indian War over here in the US). The first large pitched battle in the war was the Battle of Bunker Hill, which saw the British lose some 300 men, with another 700 injured, including a fair amount of officers. Reportedly, Lord William Howe, the British general in total control of the North American Front, said after the battle, "Another victory like that, and the American's have won this war!". Despite losing Boston to George Washington, however, the rest of the year 1776 will see American defeat, after defeat, until the Battle of Trenton and Princeton in New Jersey, but by 1778, the British will take Philadelphia, much to general John Burgoyne's dismay, after finding out William Howe had left his army for dead in northern New York; Saratoga, the changing point of the war. Another large part playing against the British was the long distance travel, and the incompetence of Lord George Germain. Lord Germain was in control of the war effort in London, and was in control of relaying the messages between the King, and Generals, and overall, overseeing the War Ministry in the UK. However, there arises a problem when not only does it take considerable amount of time for messages and supplies to travel across the Atlantic Ocean, but that Lord Germain had no understanding of the political situation in the Americas, nor it's geography. For example, he gave unclear orders too William Howe during General Burgoyne's Saratoga Campaign, which Howe really just discarded anyway, and went on to capture Philadelphia, believing that it would help force the capitulation of the American Congress. He also led the generals to believe that the British would receive a large amount of public support from the Americans in the southern colonies, which is why after 1780, the war abruptly switches from battles and focuses in New York, Pennsylvania, New Jersey and Connecticut, and shifts down to Georgia and Carolina (the war will end in Virginia, the Battle of Yorktown, on the coast of the Chesapeake Bay). But the British found no such friendly reception, having a hard time forcing there way out of South Carolina. With Washington still stuck in Valley Forge in the north, Nathanael Greene, was put in place of the Southern theatre for the Americans, and proved to be quite an able leader. So by the time the British pushed out of the Carolinas, the French navy was already stationed in the Caribbean and the Thirteen Colonies. Public support from the Americans further declined after the British General Tarleton massacred an entire unit of Americans that supposedly surrendered, either rejecting or not receiving it. The event stiffened American resistance, making a lot of Americans weary of 'Tarleton's Quarter'. And finally, of course, French intervention cannot be understated. Initially supporting the Americans through a fake company that was importing 'food' and other stuffs to the Americas, the French used it pre-Saratoga to smuggle precious gunpowder and ammunition to the Americans. Finally, after the French arrived, they helped surround the British army at Yorktown, forcing the British to give in to America's demand of independence, once and for all.

In conclusion, I believe that had Saratoga not taken place, then the Americans would have been royally screwed. After the unfortunate Invasion of Quebec by America which saw the loss of some 1,000 Americans and a very promising leader, Richard Montgomery, America was running low on resources, morale, and men. The Congressional Army also had to face the problem with soldier contracts which only lasted one year, until they could leave and return home. By the end of the Siege of Boston on March 17, 1776 almost 15,000-20,000 troops had made up General Washington's Army. After their defeat at Long Island, Washington marched down New Jersey with 5,000 men at best. Only after Washington's victory at Princeton did men regain morale, but it still didn't help the fact that they had little to no gunpowder, artillery, or munitions. Without French intervention or some other foreign power, the cause was hopeless.