I agree with the first two comments - you should be able to execute a Deed of Gift that describes the donation in very general terms and still allows for weeding as it is processed. If, however, you would feel more comfortable with a detailed, itemized Deed of Gift that is signed after staff has gone through the donation, you can accept everything under temporary custody and do final paperwork later like you would normally. In that case, you could speak to your donor about connecting you with who would be the executor of their estate should they pass before the donation is complete. I've had about five donations total where the donor passed away suddenly while everything was still held under temporary custody - it seems really daunting at first, but it is usually as simple as getting a signature from a relative and the families I've worked with were all happy to help.
------------------------------
Whitney Broadaway
Director
Southeast Museum of Photography
Daytona Beach FL
------------------------------