Even if it doesn't actually fail and fall out and make you eat pavement it will still have a couple of problems. Being smaller the quill will flex more easily and this will allow the epoxy at the joint to fail. Since part or all of your upper headset components will be supported by the bit above the joint it's going to allow the bearings to flex out of alignment and wear away at parts of the cup and cone far more quickly than normal. On top of that there's a good chance that the levering action of the flexing will make the glued portions creep and you'll continually be fighting with loosening headset issues.