Best practices for updating abandoned addons?

[Tazmyr]

I'm an addon author, and have been asked by a guildie to make updates to an addon that appears to have been abandoned. I'm awaiting a response from the author, but in case I don't hear back, what are the rules and best practices for handling this?

FWIW, the author has no license file or text accompanying his addon, so we're working from whatever is the default license stance.

Is there a way to "assume" an abandoned addon, or should we re-publish under a different addon name as I've seen done with others? (Maintaining original author attribution of course)

TIA for your wisdom.

Taz