Chauncey Billups is back in the fold for the Knicks next season, but there is no guarantee he will finish the year with them. Yesterday's decision not to buy out Billups, despite his nightmarish, injury-wrecked playoffs, is a no-brainer on several levels. Billups' trade value could be significant next season if the Hornets put pending free agent Chris Paul on the block at the trade deadline or the Magic try to trade Dwight Howard before he reaches free agency next summer. The Knicks have a paltry amount of trade chips as it is. Billups will make $14.2 million next season, an expiring contract for a player still considered among the top 10 point guards in the NBA. In another scenario that Billups would love, the Knicks could deal Billups back to his hometown Nuggets this summer in an attempt to get back restricted free agent Wilson Chandler and Raymond Felton, neither of whom is happy in the Rocky Mountains. The Knicks, as reported in yesterday's Post, have an interest in trying to woo Chandler back to New York. Billups now is set for next season, team president Donnie Walsh appears set to return — a new deal could be finalized by week's end — and coach Mike D'Antoni may know by tomorrow that he is returning, too. Knicks owner James Dolan is preaching stability more than ever following another season of roster upheaval created by the Carmelo Anthony trade. In the wake of The Post's report that Walsh is expected to return next season, the Knicks president made the announcement Billups will be kept. Billups could have been waived by tomorrow's deadline and bought out for $3.7 million. The savings, however, would have brought the Knicks under the salary cap by, at best, $8 million, and they would have been in dire need of a point guard amid a bare free-agent crop.