does anyone know the rule if enough players foul out of a game
leaving only four players left what happens? does the last player to foul out get to play?

No, they would play would 4.

But that'll never happen, why worry about it. :)

If there are no remaining players, the player stays in the game, and each foul by that player will be treated as a technical foul.

Not in the NBA, Tony. That wasn't in the post, but it was in the title of the thread.

NBA Rules DO NOT allow anything less than 5 on the floor

RULE NO. 3-PLAYERS, SUBSTITUTES AND COACHES

Section I-Team
a. Each team shall consist of five players. No team may be reduced to less than five players. If a player in the game receives his sixth personal foul and all substitutes have already been disqualified, said player shall remain in the game and shall be charged with a personal and team foul. A technical foul also shall be assessed against his team. All subsequent personal fouls, including offensive fouls, shall be treated similarly. All players who have six or more personal fouls and remain in the game shall be treated similarly.
b. In the event that there are only five eligible players remaining and one of these players is injured and must leave the game or is ejected, he must be replaced by the last player who was disqualified by reason of receiving six personal fouls. Each subsequent requirement to replace an injured or ejected player will be treated in this inverse order. Any such re-entry into a game by a disqualified player shall be penalized by a technical foul.
c. In the event that a player becomes ill and must leave the court while the ball is in play, the official will stop play immediately when his team gains new possession. The player shall be replaced and no technical foul will be assessed. The opposing team is also permitted to substitute one player.

I never read the titles. :D