Onus :
If Pascal is that much more powerful, then at least initially, it will be priced accordingly, otherwise it immediately obsoletes multiple prior generations, which will be stuck on shelves forever unless they're sold at a big loss.
If nvidia had a monopoly, i would agree with you. But with AMD Polaris looming around, nvidia cannot overprice, or they risk losing a big chunk of the market to AMD if Polaris is cheaper.
The most sensible choice IMHO would be for nvidia to implement a buyback program and buy the unsold cards in exchange of credit for Pascal hardware. Then refurbish and sell those cards to OEMs that can move that stock of less appealing hardware.
In any case, it also depends that Pascal has good yields. If availability of Pascal is limited, everything i've said doesn't matter.