This would indicate wherever they were hosting their site on no longer exists. 503's even on pages that should mostly be static suggest the backend no longer exists, or whatever ingress they're using in front of it disappeared. As far as I can tell every single page on their site is 503'ing.

Example of a response I see:

< x-cache: Error from cloudfront < via: 1.1 bdf85d6d4811ab08c57841855a848f8a.cloudfront.net (CloudFront) < x-amz-cf-pop: LAX54-P11 < x-amz-cf-id: nTQ-y1Ut3F-04jUCDM09ordCtj0CMkVmmtZTe__BtzEr1sMJu7rKaw== < age: 76773

Speculating wildly, they got pwned and are having to rebuild the site from barely-existent out-of-date backups? As others have pointed out, a failed migration doesn't take you out for this long, you should be able to roll back unless your migration plan was "reformat and reinstall".