As many have pointed out, the Rangers do not retire numbers easily -- and neither should they. I don't like teams who retire too many numbers, personally.
Jagr quite simply won't get his number retired by the Rangers, but that's no knock on him. Like Edge said, anything less than starting a dynasty won't be enough.
As for Leetch, I believe he will get his number retired. He more than anyone (even Messier and Richter) was the quintessential Ranger for more than a decade. He's like Rod Gilbert that way, and I think that gets his number retired.
Even though I would like to see number 9 in the rafters, too, but the Rangers being as they are, I don't even think Gravey is going to get his number retired and it doesn't bother me very much.
Leetch's number raising ceremony will happen, I believe most likely right after he retires. Which goes to show you how tough it is for a Ranger jersey to be retired. You had Brad Park wearing #2 for nearly 8 season, averaging somewhat under a point per game as a defenseman; 3 first team All Star selections, and a wildly popular captain. It would be interesting to see #2 go up with both players at the podium.