i think mark just did not want to answer that question. he could say "i don't want tom back again, so he can't get back to the band ever", or "well, maybe in the far future the band will need him, or maybe he will really want to be a member again, then we can talk, the possibilities aren't closed". in one case he would seem selfish, on the other the fans would speculate... obviously he doesn't want this insane version of tom back, but as it was discussed here a lot of times, if tom would go sane and would be able to act like a real member, there would be no point of having him on the ban list. the chances are slight for the latter.