It's a completely legitimate option for a number of reasons.
1) Obtain Paul...Paul leaves, KG and Ray expire, and the only salary you're committed to is Pierce. No big free agents have ever signed in Boston -- EVER --, so you're looking at a team of Pierce and scrubs. With any luck, you trade him for a pair of first rounders.
2) Keep Rondo and extend Green, KG and Ray expire, and you move forward with Rondo, Pierce and Green. AT BEST you're a 6 seed with this core. You wont win the atlantic with the Knicks and 76ers growing stronger. Stuck with early 20's picks for the remainder of Rondo's contract...You're just putting off the inevitable rebuild for a few years.
3) Blow it up at the deadline this year when you realize the old guys can't win a title together (assuming you dont get Paul). Acquire as many picks and young players as possible for the 'big' four. Start the rebuild immediately while your players still have value.
4) In the off chance you get lucky, you get Paul...and he convinces Howard to come on board and you move forward with Paul, Pierce and Howard. Best scenario, obviously.