The intention in the script is Roth's assassination is in 1960, and the final scene, of Michael realizing he's lost everything, is set years later in Autumn 1968, interwoven with the flashback to 1941, and the film ends as it does with that shot of Michael alone. No attempt is made to seem that Roth lived until 1968; even in the script he dies in 1960; we simply jump forward in time at the very end to when Anthony is 18.

And in the finished film as it stands, in that last frame, when Michael is looking back at a turning point in his past, and seeming to consider all that has happened since 1941, he DOES look different and noticeably older than the 1960 segments with Roth, which is why I believe that last scene is still 1968.

In that scripted ending, Michael is already sickly with diabetes by 1968 (which the film hints at earlier by his consumption of that pill and eating sweets) and Connie is taking care of him in what the script describes as a "sister-wife" sort of way. You can see the differences in his age in the two scenes even in the finished film, the wrinkles added to under his eyes, slightly greying hair and subtle wrinkles to his hands for a 48 year old Michael.