We do not have any other users experiencing the issue you have described. According to our records order #:4087 expired on Dec 2, 2016. Did you purchase a new key or have proof of renewal?
To renew, login to the account and click the Renewal link on the left.
Regarding your questions;
a. This was our first outage in two years, nonetheless we will look into our options for a backup server.
b. You may renew at any time.
c. Yes, if you install PDFtk on your server you will still be able to use the plugin. (Except merging signatures, images, and the Unicode font)
We remain at your service.