I think if your project goes dormant for years, and was never really that big of a thing to begin with, that you kind of give up naming rights, don't you?
The original Hyperscript still gets talked about, at least in the React and Solid communities and if only in conversations about the relative merits of different rendering methods. I wouldn't feel comfortable naming a project Zepto today. Why muddy the waters unnecessarily?
I'll admit those aren't my circles, so if I'm wrong to say the older project never hit critical mass, I'm sorry.
Hyperscript still has mindshare as a syntax even though it doesn't as a project. It is often an (sometimes indirect) inspiration for syntaxes used by microframeworks.
Not saying this directly applies, but under the Lanham Act, nonuse of a trademark for three consecutive years is prima facie evidence of abandonment.