Tulowitzki recently passed Matt Holliday, who had 17.5 bWAR and 22 fWAR while playing for the team from 2004 to 2008. Had Holliday stayed with the team to build on those marks, he might have stood a chance at climbing even higher up the team's record books. However, since he will be with St. Louis for the foreseeable future (“the foreseeable future” being through 2016 or 2017, in this case), his chances of having his number retired in Colorado seem slim at best.
On the subject of former Rockies who now play elsewhere, Ubaldo Jimenez stands atop the pitching bWAR leader board with 17.8 (for reference, he also had 20.3 fWAR while with the team). Even if he were still with the team, his case would look rather precarious, as he seems to have flamed out over the past year after peaking in 2010. Also, it appears that he may have burned some bridges in Colorado, further damaging his case. Jimenez wore No. 38 while pitching with the team from 2006 to 2011. He may get some sort of bonus for being the team’s first true ace, but I doubt that will be enough to overcome all the holes in his case.
Following Jimenez on the pitching leaders list is Aaron Cook, and as solid as he was (15.4 bWAR from 2002 to 2011), he was hardly ever great.
Returning to the position players, Blake Street Bombers members Vinny Castilla and Andres Galarraga follow Matt Holliday on the WAR list (Castilla is fifth on both lists, while Galarraga is sixth in bWAR and seventh in fWAR). Castilla spent nine years (1993 to 1999, 2004) with the Rockies while posting 15.9 bWAR, 18 fWAR, and some wildly-inflated pre-humidor numbers. While his run with the team was solid, No. 9 does not stand out the way his teammates Helton and Walker did. Galarraga is similar: impressive-looking yet inflated numbers, and decent but not great value (13.4 bWAR, 14 fWAR). On top of that, he played even fewer games with the Rockies than Holliday.
I suppose it’s worth mentioning Dante Bichette at this point. However, he didn’t play with the team as long Castilla (only seven seasons, 1993 to 1999), and his value was far less (3.1 bWAR, 8 fWAR). I don’t see the team dropping this far down the list for candidates.