There's no guarantee Hilary would have won in 2008 or 2012, so no.
Don't be ridiculous. She definitely would've won in 2008, particularly after the financial crisis. The only debate is if she would've done so by a bigger margin than Obama (and I think she would have, since Appalachia was still open to white Democrats at the time). 2012 could plausibly have gone differently though.
Anyway yes, as you mentioned, I've always thought it should've been Hillary 2008/Obama 2016, for all the reasons you mentioned plus age. It wouldn't have been a problem for Obama in 2016, but it's a slight one for Hillary now.
I agree that she would have won bigger than Obama in 2008, probably by an Ike 1952 margin. But she would have likely lost to a competent R in 2012. Any base problems would have been fatal to a Democrat in the 2012 environment because independents just weren't satisfied with the economy. Unless you think the economy would have recovered faster under Clinton, she wouldn't have made it to a 2nd term. Whether Obama could beat the incumbent R in 2016 is unclear.
