I think it was stated in Nemesis that B4 would never fully integrate Data's datatransfer, his technology simply was to...simple, compared to Data.
As for the half humanoid/half positronic brain, that was Vedek Bareil. He died a few days later....
An obstacle VERY easy to overcome by two whole sentences of technobabble.
It happened at least twice in tie-in fiction; both times, it was underwhelming (despite the technobabble being convincing by trek standards).
If that's your argument for Data's resurrection not coming to pass...well, they say 'hope springs forever'. Of course, 'grasping at straws' is more appropriate as a saying.