As sad as I am about Tosh and Owen, I really don't think it would be right to have some kind of reset button to bring them back. It would cheapen their deaths, and their sacrifices. So I'm not going to be joining the fans who plan on hitting RTD with emails begging for their returns.
I do believe we will see Owen again somehow, though...I don't think a reset will be necessary in his case, who knows what the radiation really did to him? Maybe the King of the Weevils will come into play again somehow. Not just living on a boat in the river De Nile, either, just that it's Torchwood, and weirder things have happened!
Tosh, on the other hand, I'm sure is really and truly dead. I do hope we see her in a flashback or even a parallel universe, though. Assuming we even get a third series..
For now, I think the Torch Sticks say it best: