Morning (again),

Hard to say. I'd guess the prices would drop initially what with people wanting 'the latest-greatest' only to rise afterwards with the rarity and obscurity.
I sort of have the feeling a 2021 or beyond XLR won't really happen though. I'd be surprised. The XLR was not a great selling car and sad to say, unless <whatever> they come up with happens to be of the electric variety, I'd wager people would just buy a new Corvette... which is already happening as we've seen with a few XLR owners already.
It's unfortunate to be at this point in automotive history - when the gas powered car is basically on the way out. I don't think (in our lifetimes) we'll ever -not- see gas powered cars, though the ones that we do will be the odd man out, highly taxed and probably shunned by the later generations.
Understandable in a way as the damage they've done to 'Mother Earth' has truly been significant, just a bit sad things went the way that they did, especially in regards to their current disposable design and such a tremendous population increase worldwide.