Sadly suicide (or even murder or accidental death) and ending up on the streets would account for some, even ending up say mentally sectioned depending on state of mind though to walk out of your life like that, something must be horribly wrong.
They have found a number of people in the rivers/canal round here recently, some more immediately than others. One lad they had been looking for for weeks, not long before Jo Yeates but there was nowhere near the publicity, similarly with another lad back home who there have been campaigns about to get his disappearance more publicity. There was another gentleman's body found recently, he disappeared, they found his car and took a while to find him.