Makes me wonder if a bunch of the world's smallest flightless mammal (a fraction of the house mouse's mass) were released at altitude, would they survive? (Not proposing that this be done but thought experiments and/or simulations):
For them other than the cold a drop from 1000 metres is the same as a drop from 10 metres.
However, shrew blankets change the whole scenario to irrelevance--a shrew in a blanket sufficient to keep it safe has very different aerodynamic behavior than a naked shrew.