Well, most popular theory is that the doll simply dissappeared, but my own theory is (which is why I asked the question), that the personality the doll had 'dissappeared', not the doll itself. It still exists, but only as a normal doll, no talking and so on. So technically it could come back, with my theory. But that's only mine, and the writers didn't tell us what "officially" happened. *barbecues them*
XD Actually, your first suggestion, Zammy, is what happens in my fanfic. (Well, almost, Sabrina tries to live with the doll but later, they pretty much make each others 'life' hell...and try to kill each other, but that's another story...)
I can't completely decide on something. I could imagine Sabrina and the doll getting a long for a short time and then splitting up like in my fanfic or, dark version, Sabrina herself even creating the doll again when she's lonely and depressed and having the doll as her only friend.
That's also the only way I could see her brining back the doll and the doll coming back by itself. If Sabrina gets lonely again.
XD Agreed, Zammy. In that case, I would even help you. ^^