If the Notezilla 's cloud sync servers cannot be reached, then you would still have the local copies of the sticky notes on your Windows PC & Laptops where you can access them & continue to create new ones. You will be able to access them from smartphones too. However, you will not be able to access the Notezilla.Net web app and the syncing will stop temporarily.
Once the server is up and running, all the changes are synced back to cloud and hence all other devices.