The focus is kept on the owner. To be active, foci need to be on the person they're bound to (see "Activating a focus", p199, SR4 20th).
It works like normally sustaining a spell (which doesn't require touch either), except it's now the bound focus doing the sustaining.
I'm not entirely sure about SR4, but the sustaining rules don't mention needing LoS. Spells normally only require LoS on casting (and only if it's, well, a LoS spell, not a touch spell); I don't see why you would need to sustain LoS after casting, especially for a touch spell.