My understanding of it has been "look, I reinvented cgi-bin."
And thus, it can be distributed as well as any other stateless function.
A cgi-bin is as highly available as the web infrastructure hosting it, which as the cgi-bin author you don't need to know anything about.
A cgi-bin cannot "crash" because there is nothing long-running to crash. It is only run on demand.
I think it is easy to make the case that CGI was the proto-serverless api and that the serverless offerings we have today are an evolution of the CGI approach.
edit: typos
If our code crashed, the next request would just get served as normal. If Apache crashed or a frontend crashed, another one would just take its place. High availability cgi-bin is trivial.