From the Eldritch Moon launch notes:

While a meld card is anyplace apart from the battlefield … it has solely the traits of its entrance face.

So as soon as a melded creature is within the graveyard, the 2 components have their front-face identities solely and don’t “bear in mind” that they’d been melded. Anything attempting to maneuver the playing cards again at hand or battlefield should work together with them individually.

However, a creature that’s rescued from demise with regeneration by no means truly leaves the battlefield in any respect, so regeneration works simply nice on a melded creature. Regeneration does not imply to return the creature from the graveyard to the battlefield – fairly it (roughly) means “the following time this creature would die, as an alternative it does not.”

Here’s a part of the Comprehensive Rules on regenerate:

701.12a If the impact of a resolving spell or skill regenerates a everlasting, it creates a alternative
impact that protects the everlasting the following time it could be destroyed this flip. In this case,
“Regenerate [permanent]” means “The subsequent time [permanent] can be destroyed this flip,
as an alternative take away all injury marked on it and faucet it. If it’s an attacking or blocking creature,
take away it from fight.”

While the melded creature is on the battlefield it counts as only one creature, so a single regeneration impact can put it aside (you do not have to regenerate each halves).