Dead bats :-O
This is concerning. Two possibilities occur to me, both of which warrant further investigation. You hit on the disease concern, which is possible, but hopefully not the case. The multiple deaths in 1 roost make me wonder if the bats are feeding on something that's affecting them. Have you by any chance collected (wear gloves!) and fresh-frozen any of the dead bats? Regardless, I recommend that you call or email Dr. Julia Burco (Julia.D.Burco@state.or.us) , OR Dept of Fish and Wildlife vet. She's very easy to talk to and will be very interested to learn more.