“Temporarily out of service”

Remove the index.html from your root directory ??
(your blog is there: https://www.heardworld.com/higgaion/index.php)

Thank you! I discovered the index.html file a few minutes after posting this. How did it get there? Was it perhaps created during my attempt (which failed) to import old Blogger items?

Most likely – yes.
I don’t know what “failed” in your import attempt… but most of the files ready for import are there:
https://www.heardworld.com/higgaion/2005_11_01_archive.html

Argh.

I deleted the index.html file this morning.

I haven’t touched the blog since then.

Now it’s back.

Why is WordPress created this index.html and taking the blog out of service?