Doesn't really matter. If the price of Bitcoin is below the cost of electricity and labor required to mine it, then it's irrelevant that the card won't be as productive (lose money at a greater rate) in future. You're still losing money either way.

The only valid reason to continue mining would be that you expected that the price of Bitcoin would exceed the mining costs in the future. Then you would stockpile them and take advantage of the reduced hashrate as other market participants exited.