I agree that is one of the downsides to DTube, I read back when I first started uploading that they only stream videos for so long, based on a formula of how much data (size) the videos uses, and how much steem the video earns.

I don't like that the videos disappear after a while, but I kind of accepted that DTube is smaller than YouTube and doesn't have the resources to keep this stuff forever.
I'm glad that my old posts to DTube don't completely disappear, as I consider the description, thumbnail, and comments to be an important part of my video history, but I always felt they should replace the run-time numbers on the thumbnail with some kind of indicator that the video will no longer stream from DTube.

I've read somewhere it's possible for people to stream their own videos from their own server, but that is not something with in my abilities.

On the other side of this, I have accidentally uploaded the same video more than once, with out issue. One of my older videos (previously uploaded to YouTube before I knew about DTube) I uploaded to DTube, then months later I had forgotten that I had uploaded it, and uploaded it again, same title, thumbnail, and everything. Later I realized oops, I had already uploaded that video, but I didn't feel too bad about the mistake as the original upload was no longer playing.

When I first discovered DTube I decided to make effort to upload to DTube before anywhere else, and make DTube the main place for any video upload... I don't have a big enough following for anyone to really notice where I upload 1st, still I wanted to make it so that I used DTube before any other place (like YouTube) ...however, I eventually gave up on that, and instead when I post to DTube I include links to other places I uploaded the video, so if it no longer plays on DTube, then the DTube description, and related Steemit article will include links to alternate versions.