Nobody, including the head of DL's RM/IM could tell you whether lower fare buckets will be released. If DL can sell those flights at the higher fares, it will do so. If it can't, it will open lower fare buckets.
Whether that happens is unknown, particularly in light of the COVID-19 situation. But, as a general matter, lower fares won't open until roughly 90 days out. But, on the other hand, maybe the flights will be sold out and there won't be any availability.
One of the things to consider this year is that unlike during the financial crisis when DL chopped its fares to sell seats, DL (and other carriers) will use smaller aircraft and chop frequencies to reduce supply if it comes to that.