For the most part, it's the same deal with a handful of other things. Marble Madness II / Marble Man is known to be dumped, but due to certain past agreements with Scott "HoardStuff" Evans, it will most likely never be released. However, it seems pretty clear that some folks are gearing up to release an FPGA version of Marble Madness II / Marble Man, so I doubt that the ROM set would stay hoarded for very long once someone picks up such a board.
Meanwhile, Variant Schwanzer (an Aleck 64 prototype) has been kept under wraps at the request of ShouTime, because apparently the owner wanted to investigate making "re-creation" (read: bootleg) cartridges. Since it ended up not being possible due to the reliance on a Seta custom sprite chip on the cart itself, it never seems to have seen the light of day. However, speaking only for myself and not any other devs who have also seen the dump, given the level of malfeasance with which the guy has conducted himself over the whole Cave CV1K thing, I'm wondering if perhaps the game might magically find its way into MAME regardless. Burned bridges have a weird way of getting charred at both ends.
At the very least, the fact that these games are archived, and presumably backed up in multiple places, gives some level of confidence that they'll eventually see the light of day. Maybe not in Al's lifetime, maybe not in Frank's, maybe not even in mine, but the fact that dumps even exist puts the situation head and shoulders among the fuck-fest that the collecting scene used to be, with people purchasing prototype carts solely for the purposes of ensuring that they would never be dumped at all.