Does the text of a Herald (or a Guardian?) continue to apply during the Final Battle?

The King In Yellow Herald with Glaaki is the only instance I can actually find that it would matter either way ...

IIRC, there's a rule that Heralds are basically removed from play when final battle starts. It's probably in the rules from King in Yellow.

I'm not aware if there is a similar rule for Guardians.

When all else fails, read the rules:

"If the Ancient One awakens, return the Herald sheet to the box, as it has
no further effect on the game."

I guess it's not in the Kingsport rules, but it's in the King in Yellow rules, so I'm sure you can assume you do the same with Guardians.