Nah, it's very possible that the Democrats never win again - but by then a new center-left party will have emerged and people will want change. There is no such thing as a permanent majority in Democracies.
Assuming we call Israel within the Green Line a democracy, there is a strong possibility the right-wing coalition will retain power for as long as the state (as we know it) exists.
As for the topic at hand, I highly suspect voters will be so fed up with Republicans by 2024, at the latest, that they will sweep in Democrats with an even greater mandate than 2008. Democrats might even win back the house in spite of gerrymandering.