Paul Pierce has been saying for a couple of years now that he has to evaluate after each season whether he wants to go on. This time around, he appears to have decided he’d like to play at least one more year. However, he knows that, because of circumstances, it may not be in a Celtics uniform, though the captain would like to remain on the only NBA ship he has known. “I’ve always said I want to end my career as a Celtic, but, you know, I have a year contract for next year, but it’s not guaranteed,” Pierce said before yesterday’s shootaround at Madison Square Garden for last night’s Game 5 against the Knicks. “So the decision is in their hands. “But whatever decision they make, you know, maybe if they trade me somewhere or I end up somewhere else, maybe it could be a situation where I come back for a one-day deal and retire a Celtic.” The Celts, down 3-1 to the Knicks in this first-round series, were aiming to get to a Game 6 tomorrow in Boston. So Pierce isn’t looking too far ahead. “You know, truthfully, I haven’t put too much thought into it,” he said. “I mean, the organization’s going to do what they’re going to do. It’s nothing that’s stressing me out. I mean, that’s what it is. Every year, they’ve got decisions to make, and those are their decisions, so I leave it to them.”