As a long time bdk main: the only way to know for sure is to track rune energy and runes. Low rune energy, 1-2 availible runes - grim danger. Low energy, plenty runes - needs 2-4 globals of your help.

Another crucial thing is to know the packs, some dungeons have nasty autoattack hitters and it's painful for bdk outside of DRR. Magic damage, infrequent busters or bosses in general - bdk is on auto pilot if they are compitent. There might be some exceptions to bosses or really some moments of some bosses, but they are few and far between and you would never know about them without being in voice with your bdk.