Could the Americans have won the revolution without the help of the French?

The French (along with other continental European advisors) were incredibly important in helping the Americans convince the British that their struggle for 13 mainland colonies was not worth the financial investment. Although unpopular in the United States, it's imperative to remember that despite its large population, the mainland colonies were less economically valuable to the British Empire than were its holdings in the Caribbean and the Indian Ocean. As Andrew Jackson O'Shaughnessy emphasizes in Empire Divided, had the Caribbean colonies rebelled [an unlikely event given their reliance on British troops to suppress possible slave rebellions] the British would have focused the majority of their efforts on the islands rather than on the mainland. Furthermore, political opposition to the British war in the colonies was strong in England. Washington's French advisors better understood the global politics of the American Revolution than did the nation's chief commander and advised him on policies that effectively won the war by breaking the British will to fight.

While American leaders were intent on striking a critical blow to British troops stationed in major American cities like New York, French advisors better understood that the Americans did not need to win a major battle or defeat the British troops, they simply needed to outlast British efforts. As Richard Van Wyck Buel Jr. demonstrates in his book In Irons, even following their surrender at Yorktown, the British could have held on to the major costal cities for decades. Partly due to his own pride, Washington was insistent that the Continental Army march on the British headquarters at New York. While the French fleet had cut off supplies and reinforcements for British land forces at Yorktown, they would have been significantly outgunned in a naval assault on New York. [They had learned this exact lesson in 1778 when the French navy had first assembled to attack Newport, Rhode Island. Although the French outgunned the British at Newport, the British controlled the harbor and an outright assault was challenging. While staging the attack a gale demasted a number of the French ships and they sailed for Boston rather than support the ground invasion.] French advisors convinced Washington that such an attack on the British was ill-advised and pressed him to sue for peace which was reached reached in September 1783.

TL:DR- French military support, especially their naval presence, gave the Americans a fighting chance against the British. It was their understanding of British weariness, however, that really benefited the Americans. French advisors convinced Washington that he did not need to defeat the British so much as wear them down.