I, for one, think Dubenko is a very important character. I would say the reason Leyland Orser is not a full-time cast member, is, he does not want to be.
He, no doubt, has more control of his time that way and has time to do a lot of other projects.
But back to Dubenko, I am sure we will see some sort of closure for him. But we have already seen him make life choices such as his decision to return to county when he realised that it was his second home.