Lieberman is a bit of an exception in any case, since he happened to represent a state that permitted him to run as a candidate for both the VP and U.S. Senate. If that were not the case, I think he would have disappeared as quickly as someone like Ferraro had. For him to come back four years later and have such a dismal showing in the Democratic primary campaign was all the evidence you need of that.
Saying that some of these people would have ended up in their future positions seems to contradict your assertion that being a losing VP candidate is a political death knell b/c if it was, then they would not have gone on to their successful careers. As for Lieberman, his dismal showing in this year's primary was b/c he's out of step w/ most Dem primary voters, especially on the War in Iraq.