There's something very ironic about the whole pass-your-hand-through-a-solid-object trope. As with TMP's "The Next Phase" and STARGATE SG-1's "phase out"/cloaking trope, one has to wonder: if this altered state makes you invisible and/or unreachable, or able to pass through solid objects, how come the ground/deck you stand on effectively stops you from drifting through the floor/ground?
(The reason I suggested gravity boots wasn't based directly on canon; it was retconned based on the way Kirk and his boarding party seem to cautiously move about while on-board the derelict. I just retconned that in from TMP6 and FIRST CONTACT.)
So, are we assuming that the violence resulting from the brian-tissue-disease-induced madness is what killed the Defiant's crew, and that this brain-tissue-distortion is not conclusively
fatal? FWIW, I have no problem with most of the crew beating each other to death, and maybe someone depressurizing the ship during the Defiant's "last days" (or maybe the life support system just went offline after there was nobody left to maintain it).
There is also the possibility that even a fully-functional Federation starship, left in this area of space long enough, may be affected by the spacial distortion. Maybe if you leave the ship there long enough all the ship's systems will be knocked offline and/or powered down. If the distortion can have an effect on brain tissue, why wouldn't it also affect the ship's sensitive instrumentation?