I've once had a whole sector of a fintech go down because one DevOps person ignored daily warning emails for three months that an API key was about to expire and needed reset.
And of course nobody remembered the setup, and logging was only accessible by the same person, so figuring out also took weeks.
I'm currently on the other side of this trying to convince management that the maintenance that should have been done 3 years ago needs to get done. They need "justification".
Write a short memo that saying you are very concerned, and describe a range of things that may happen (from "not much" over medium to maximum scare - lawsuits, brand/customer trust destroyed etc.).
Email the memo to a decision maker with the important flag on and CC: another person as a witness.
If you have been saying it for a long time and nobody has taken any action, you may use the word "escalation" as part of the subject line.
If things hit the fan, it will also make sure that what drops from the fan falls on the right people, and not on you.
And of course nobody remembered the setup, and logging was only accessible by the same person, so figuring out also took weeks.