When a significant player leaves, just hold his number out of circulation for a while until clear heads can decide if it should be retired or not. Just saying HOF is kind of dumb because there are players who play a significant role in their franchise's history for reasons other than HOF caliber play that should be considered...
This always bothered me about the Cubs, who used HOF as a requirement, until they finally put Santo's 10 on the pole at the last game of 2003 when they thought he was near death. All while pitching him for HOF. Seems backward. If he's one of your franchise's greatest players of all-time, honor him that way. Don't let the HOF decide.
Then there's the out of circulation issue. The Cubs were smart and kept Sandberg's 23 out from the day he retired. But then there's the 31 mess created by the dual issues of not holding out Jenkins and then deciding to honor a Brave to make up for their own stupidity. Mark Grace might have been a guy worthy of Cubs consideration but not HOF, but they issue 17 to call-ups as if there aren't enough numbers to go around (Bobby Hill, Pie, Fontenot, Garza). They were quick with 21 as well, considering Sosa was the all-time team HR leader and part of two playoff teams. Low standards, but they can't keep retiring 1969 Cubs and part-timers. And they are the Cubs.
Flying a numberless flag or commissioning a statue for an actual World Series champion and not someone who finished 8 games out of 1st might be a good idea at some point, too. But I just know they're itching to retire 34... ugh.