Seriously, we've brought Kirk, Spock, Tucker and Janeway all back from the dead. Why not Data? Believability shouldn't be a roadblock as it got thrown out the window a long time ago in the Star Trek universe.
Besides, TNG never felt right after his departure.
Well you need to get a Face Book page, and about a thousand (give or take some) working fans, a twitter account, and a petition. Then just never ever give up.
Seriously Data should be brought back, the reasoning behind a plot ending in his death while valid at the time are not today. He is a great character and he should be returned.