You're right that it's all up in the air right now, but your last paragraph says it all. NVIDIA doesn't have to be aggressive and give you that value, but AMD is a big question mark at the moment. They definitely have to be more aggressive than NVIDIA, and it's very possible that they will try to reclaim as much market share as possible.
Sure. I guess it depends on what AMD sees as a priority- having the top card or hitting the sweet spot?
If it is the former, then we will see a Fiji replacement first. I think there is actually a good chance this might happen, given how they really wanted Fiji to take back the performance crown from Nvidia's Titan (it just fell short). The problem with a Fiji replacement first is Fiji is their newest chip, heck they haven't even rolled out its full lineup yet. One good thing about a Fiji replacement is current Furys can be marked down to where the 390x currently is, killing two birds with one stone. AMD doesn't have the resources to make a new card for every tier, something will be a rebrand.
The sweet spot move is obviously replacing the 390 and 390x. This would match up well to a 980 replacement, and give the 970 (which is currently the biggest hit on the market) a reason to sweat, but it would hang Fiji out to dry (the gap between the 390x and the regular Fury is already too small). I really don't think AMD is going to do this, which means Nvidia gets to sell 970s into 2017. The 390 is doing well right now and wasn't launched that long ago. You have to figure the midrange will eventually have 4GB HBM, but that will look bad next to the 8GB 390 unless it blows the 390 away.
The dark horse is AMD releases the Tonga replacement first. I think this is the best move for them- the 960 is a VERY weak competitor and Tonga is getting a little old at this point (even though we just barely saw it in full form). I think the gap between the 380x and the 390 gives AMD more wiggle room than anywhere in the market. We could get a Tonga replacement that is an upgrade that doesn't knock off the 390 and as a bonus it might be toe-to-toe in Directx 12 to the 970.
We will know soon enough. One thing is for sure, anyone assuming the 980 ti replacement out the gate will be disappointed. No matter what AMD does Nvidia is going to want to milk another Titan before it destroys that value with the 980 ti replacement. Unless AMD is super aggressive (more than a company in their condition can be) OP is waiting until 2017 to buy a new card.