I don't think we will get any sort of confirmation regarding Billy Miller.
I think it will be similar to Stafford.
He will appear on screen serving as confirmation.

I would love to see flashbacks too.

I do want to see the love story play out.
I don't know if that is in the cards.

I would love for real Jason to reach out to Liz for help.
Meanwhile, fake Jason is back.
Real Jason will know what to say to Liz and she will believe him.
The two work towards Jason reclaiming his life.