The link was available for a short while and many was able to download. If you did, the latest reports is that you're still able to do the actual upgrade. However, even the ISO of 15063 was available for download for a little while and I managed to grab it before it disappeared.
It has to be emphasized that this latest insider build gives you the option to opt out of the insider program for the first time since its introduction about two years ago. In other words, you're no longer held hostage by Microsoft with the only way out being a complete re-install of your system using the official release install.
Furthermore, the 15063 build is not time-bombed like the other insider builds and so you can even stay behind on this build if you so desire.
Upgraded one install today and it went through without problems of any kind