As long as Semper keeps those videos pinned they shouldn't disappear from the IPFS network as he keeps a local copy. THe problem is with videos which he uploaded before via d.tube's upload form which have disappeared so far although they earned.
As Semper concluded IPFS is just not "release"-ready yet with content disappearing and you not having control over it.
I'd check and see if the content behind a given Hash (which you can get from the video url by right clicking the player) is still in the IPFS network via IPFS tools.