I think your yorkie can learn to bark from another dog. Kaji never made a peep (he was 12 months when I got him) and now he barks and is noisy when we're at my friends house. (her yorkie is very vocal) He's even starting to growl at home. This is my experience anyway.
As far as how long he's alone... That's tough to say. Some aren't as lucky and can only take a few weeks off when adding a new puppy. The banging is the hardest part. Maybe they need help with training?
__________________ Littlest JakJak 
We miss you Kaji 
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