Mercer is not going to be here past next season. I just don't see him here long term. Now yes, for the short term (ie next season) Mercer can fill-in for Jack on the bench. Also, I see Bowen's role as diminishing on the team over the next couple of seasons.

A 4 year $18 million contract would start at $3.8 million in 2003-04. That's very reasonable for Jack. And that's a full $1 million less than the average NBA salary. Sure, that's guaranteed money for 4 years, but on the flip side you are locking in a talented and clutch player to a below average contract for 4 years.

A 4 year/$20 million contract would start at about $4.2 million. Still below the NBA average.

Before I forget, having a 6'8" athletic shooter who can run the floor and swing between the 2 and 3 is a tremendous asset to have on this Spurs team. There's a reason PJackson loves to have big perimeter role players...if an opponent tries to switch their SF onto your defensive SG then they won't gain an advantage (ie post-up or shoot over). It improves a team's perimeter defense significantly. Jack has fit well in the Spurs' defensive scheme.

Bowen can't play forever.