That advantage is frontcourt depth, size and skill, and since no other NBA team (except maybe the Oklahoma City Thunder) can match that, the Lakers have to keep their frontcourt depth to ensure a successful playoff run this year.
If the Lakers want any shot of beating the Miami Heat in a possible NBA Finals matchup, their only chance to have success is by dominating the paint and winning the rebounding battle.
Los Angeles doesn't have enough athleticism or bench strength to beat top contenders, so its frontcourt must remain intact.
Gasol has not played well this season, that much is clear, but the Lakers must be patient with him. Having to learn two different offenses from two different head coaches in just a little more than a month is quite a challenge for a veteran player who thrives when he's comfortable with the plays being run.
Gasol can play very well in new head coach Mike D'Antoni's offense—he just needs a bit more time to learn the schemes.
He also needs more experience playing alongside Dwight Howard. Since the Lakers haven't had a center that needs the ball as much as Howard on offense in the Kobe Bryant/Gasol era, it's taken some time for the team to re-adjust.
Having two big men is a recipe for playoff success in the NBA. The San Antonio Spurs won two NBA championships (1999 and 2003) with the PF/C combination of Tim Duncan and David Robinson, and the Houston Rockets were successful in the mid-1980s with two All-Star centers in Hakeem Olajuwon and Ralph Sampson.
You don't trade away great power forwards who excel at both ends of the court unless the return package includes a great, young talent. It's hard to imagine the Lakers being able to trade Gasol for a young player to build around in the post-Kobe era.
Despite their recent struggles, the Lakers don't rank too poorly in a number of the league's important offensive and defensive statistics.
The Lakers are rebounding well and scoring a lot of points, so there's no reason to panic in Los Angeles. As Howard continues to get healthier, the team will improve defensively, and when star point guard Steve Nash returns, the team's assists numbers will rise.
For the Lakers to make a deep playoff run, they cannot trade Gasol. He and Howard can be the best PF/C combo in the NBA very soon and just need a bit more experience playing together.
The only way for the Lakers to win their 17th NBA championship this season is to beat teams with their frontcourt depth and skill at both ends of the floor. Losing Gasol would ruin that advantage and make the Lakers a very beatable team in the playoffs.