I think it's possible that the used price will go up. I don't know that it's probable, but I think it's possible.
The used price is often tied to the new price and the new price of the A7RII recently dropped. However, it was a sale so the price of a new A7RII is about to go back up. Therefore, potentially, the used price should go back up.
IMO, the only factor which might keep the used prices low is that SO many people purchased new and used A7RII cameras in the last few weeks that demand, at least for a while, has been satisfied and therefore, to meet the new demand, the used price will have to stay low.
I doubt any new A7RII will be sold for quite a while as anyone who was on the fence at the current sale price will definitely NOT buy at the normal price.