Assuming a PoD later than 2008? Tough to imagine. As has been seen since 2006, the Democratic base in most areas has shifted left rapidly. Even if this hasn't really resulted in a lot of Democratic incumbents losing primaries (big exceptions being Joe Lieberman, Al Wynn, Joe Crowley) or just having to sweat them out (Blanche Lincoln, Dan Lipinski), it's still definitely helped to pull most incumbents left, especially recently. It also means that genuine centrist/moderate/conservative/whatever Dems aren't getting through primaries in open seats, John Morganelli's recent campaign being a good example.
I don't think "more liberals losing while moderates/conservatives win" is really viable, because in general, federal politicians try to tailor their ideological position (in terms of votes/public position taking) to their constituency. I think this is particularly true for Democrats, and while there's exceptions to the rule - Sherrod Brown being the most obvious - generally speaking a swing district/state Dem is going to be more moderate than one running in a solid blue constituency. What this means in the context of your question is that these same moderates are much more vulnerable to defeat in a general election than their more lefty peers - in 2010 and 2014, it wasn't Progressive Caucus members going down, it was Blue Dogs and New Dems. The Republicans saw similar outcomes in 2006 and 2008, which effectively wiped out the moderate faction in their congressional ranks.
Candidates matter, of course - look at Heidi Heitkamp - but only so much. Plenty of entrenched, personally popular incumbent conservative Dems lost in Republican districts in 2010, and others retired likely because they knew they couldn't win and didn't want to bother campaigning for a year just to lose. It's really hard to beat PVI.
Finally, I think it's helpful to define our terms a little bit. By and large, I don't think the moderate/conservative Democrats of 2014 are ideologically comparable to those of say, 2000 or even 2008. Mark Begich or Kay Hagan aren't exactly clones of the old school Southern Democrats.
All of that is a longwinded way of saying that unless you find a way to prevent the wipeouts in 2010 or 2014, I think the only way to do this is have a pre-2008 PoD. Perhaps if the Bush years are less radicalizing to the Democratic base (ie no Iraq war, etc), the party won't shift left as quickly. But - what would really work is preventing the defection of Southern Democrats (and more broadly, working class whites) to the Republicans. And to do that you have to go back decades.