The Donor hereby acknowledges and agrees that the Donor's obligations hereunder are irrevocable and may be enforced against the Donor and shall extend to, and be binding upon, the Donor as well as the Donor's executors, trustees, administrators, representatives, heirs, and assigns.
Briefly, whether a pledge is enforceable depends on the law that applies to the pledge.
In the U.S., it generally depends on state law, which varies from state to state, but is generally based on either (or both) of two concepts, detrimental reliance (essentially, that the organization took some action based on the pledge such that the organization would be harmed if the pledge was not fulfilled) and consideration (the donor received something of value in return for the pledge).
A web search will likely turn up more detail on how this works and the law in various states, for example:
I'm not sure how any of that might apply to your context!
My US$0.02 worthl the usual disclaimers apply.
Alan S. Hejnal (he/him/his)
Data Quality Manager
Office of Advancement
600 Maryland Ave SW Ste 600E
PO Box 37012, MRC 527
Washington, DC 20013-7012
(: 202-633-8754 | *: HejnalA@si.edu