Boone was one of the top two-sackers in the game from 2001-2003, batting a ridiculous .331/.372/.578 in 2001. He was a low-risk minor league signing for the Mets this offseason, and his retirement does little to affect the competition amongst the other three players.
Matsui is likely the frontrunner at this point, and I'd peg him at 3:2 odds to win the job. Hernandez has a shot if he plays really well in spring training, and Keppinger is a longshot at best.
YEAR TEAM AGE R H 2B 3B HR RBI BB SO SB CS AVG SLG OBA OPS 2001 Mariners 32 118 206 37 3 37 141 40 110 5 5 .331 .578 .372 .950 2002 Mariners 33 88 169 34 3 24 107 53 102 12 5 .278 .462 .339 .801 2003 Mariners 34 111 183 35 5 35 117 68 125 16 3 .294 .535 .366 .902(Stats generated using Lee Sinins' Sabermetric Baseball Encyclopedia).