My domain whois admin contact is pointing to a nonexistent email address

Solution 1:

This registrar does not have a self-service portal with a login that you can use to update the WhoIs information yourself? If not, your registrar will have a procedure for doing this, but you'll have to jump through hoops to get it.

In the past, in the days before self-service portals for this stuff, I had to send a certified letter, via registered mail, to the registrars office. The letter was on an official company letterhead, included details of the situation (in this case, a previous employee had registered a company domain under their personal account and then gone AWOL). We included proof of our company registration, and that the domain matched our company registration (and the domain was still actively pointing to the company website).

It took time and patience, but we got the domain back. You need to navigate the red tape and bureaucracy of these companies, but if the company is so small that they don't have a self-service portal, this might be easier than you think.