As another early retiree—at least, I was, for some time, before I un-retired (hopefully temporarily) to pursue an expensive startup project, as a funder—I think you underestimate the power of the FIRE’s income. By the time most of us are ready to “pull the plug”, the usual question is not, “How probable is that I never run out of money?”, but “How much time did I overspent working, since this safety margin is, with benefit of hindsight, obviously excessive?”. Thus, most FIRE types should have more than enough to maintain donation rate, and probably increase it.
As another early retiree—at least, I was, for some time, before I un-retired (hopefully temporarily) to pursue an expensive startup project, as a funder—I think you underestimate the power of the FIRE’s income. By the time most of us are ready to “pull the plug”, the usual question is not, “How probable is that I never run out of money?”, but “How much time did I overspent working, since this safety margin is, with benefit of hindsight, obviously excessive?”. Thus, most FIRE types should have more than enough to maintain donation rate, and probably increase it.
See for example, https://www.mrmoneymustache.com/2022/07/18/never-run-out-of-money/