Are yorkies okay to be left alone for 6 hours, usually Monday through Friday?
I think the effect this would have on a yorkie would depend on how old it is.
Of course the dog will survive the time alone, but it may eventually be affected in a behavioural sense.
The younger the yorkie is, the more noticeable this will be. The dog may become unsociable and even scared to interact with other people or animals.
There is also the chance that the dog will lose the ability to be house trained as it becomes second nature to do its business in the house.
An older dog might cope better in situations like this.
While it will not be possible to spend every waking minute with the dog, an effort should be made to keep alone time as short as possible.