I think almost anything can be forgiven except the lack of communication.
Even if an order has not been filled in over a year most buyers would still be happy and patient if their messages were answered and they were assured their order would eventually be filled... even if they email once a week for a year straight.
If this kind of customer communication cannot be provided, then yous might as well just shut down and give up because everyone who gives you money for your wares deserves this courtesy ...
It takes about 20 seconds to reply to an email.
If you can't spare 20 seconds per customer, then you shouldn't even be selling anything.
Just giving my opinion
Thanks