It might be instructive to find out what the marine insurance companies have to say about the insurability of engineless cruising sailboats. Perhaps their actuarial data can quantify the risks of going engineless.
Interesting question, any Insurance experts out there? Location may be a factor, out on the open ocean where it is not too crowded might be acceptable. It is possible that most boats worth insuring, or required to be insured because of a loan, are probably big enough to have an engine, with some exceptions of course, that being where an engine has been removed and not replaced.