Is this a full on 501(c)(3) non profit organization or just this guys hobby? I assume if he is taking donations, it must be legit, but you never know.
If it is a legit non profit, the annual report which must be filled every year and made public would give you an idea of how much money is coming in, how much salary (if any) he and others are receiving, and how much of a burden your expenses for transferring the website to him may be.
Assuming the organization is taking in even $250k/year, and only has a few full or part time employees and several volunteers, you shouldn't feel any guilt in taking the site down and asking the prick to reimburse you for all costs to transfer the site, all passwords, all content, domains, etc., to him, along with creating any necessary documentation for whoever is going to take it over. If the money doesn't go to you for your time, it's just going to find its way to him one way or another.