I've spent well over $2k on guitars, accessories, DLC, etc, for Rocksmith 2014. For five years I've been using it to learn bass guitar, and absolutely love it.
One day Ubi is going to turn off the servers, and I am simply going to cry.
There is no alternative I'm aware of, the new version is AI garbage from what I've heard, and I enjoy the thing I have and the songs I've paid for.
If they are not going to provide an offline mode, or the server code, then I will 100% make it my mission to pirate the game and make it playable offline.