Heh, well I waited about 4 months from when I first noticed my bearing was going bad. U can go quite a while on it, but one thing that could happen would be the bearing could sieze up, so your wheel won't turn, or it could warp, causing big damage to the axle or hub/knuckle assembly. WORST case scenario, your wheel could come off, but I don't think that would happen.
It will cost quite a bit for a new hub. When I checked for my 89 rex a couple days ago, it was a dealership only part, and Honda sells it for around $150, i think. You only need a new hub if the outer edge is damaged in some areas(the damaged edge can throw off wheel balance, and cause premature wheel bearing failure), or if there's any physical damage to the hub itself(cracks, big chips, etc.). Otherwise, u won't need a new hub. If you've been driving on a bad wheel bearing since Jan. though, I would prolly replace the hub and bearing together.
Due to the high cost, I would just pick up the entire knuckle/bearing/hub assembly at the yard. I got a 99 civic si knuckle for $75! Damn near perfect condition(aside from rust). U know a wheel bearing is good when the wheel has slight resistance when u spin it, and no noises while it's spinning.