Originally Posted by WillAdams
They can always start a new line of comics in a new continuity (i.e., Marvels ``Unlimited'' line).
DC had Earth 1 and Earth 2 back when I was collecting (as well as Earth S and Earth 0, our earth), so yeah, the Earth 1 Batman would be 80 or so and long-retired, but they could've then started up Earth 3, 4, &c.
On Earth-Two, DC did let the heroes and villains grow older, with the sons and daughters of the original heroes making an appearance. Before his death, the Earth-Two Bruce Wayne had married Catwoman, retired from being Batman after his wife's death, and his daughter Helena had taken up fighting crime as The Huntress.
I agree that the multiverse provided a simple way to clean up continuity: just shift to a new earth when the time is right. The old continuity is retained and can be revisited when desired, but you can start again on a new earth without the need for a universe-altering event. This was done with the Tangent Universe, set on Earth-9 in the current Multiverse.
DC has restored the multiverse, with 52 positive-matter universes and one anti-matter (our world, Earth-Prime, exists but is not part of the above multiverse). About half of the earths in the Multiverse have been explored.
However, based on what I've read in "Flashpoint" so far, it is possible that the entire DC Multiverse along with all of its entire history have been completed wiped out and replaced with a single universe with a new history.