Is "girls" a suitable complementary term to go along with "guys"?

"Guys and gals" isn't archaic, and I'd say it's your best bet here if you want to avoid simply saying "guys", in a casual context.

Much more formal is "ladies and gentlemen", though that would definitely not be used casually.

If you're not addressing the people but rather describing the group, they could be described as "men and women".

If you just want to refer to a group of (maybe) people of mixed gender, you could say "guys", "everyone", "people", "y'all", etc.

Normally the term comparable to guys is gals.

And I think this is one case where Google NGrams can actually be useful. Here we see that guys and gals and gals and guys clearly outnumber girls and guys and guys and girls.

Note that girls by itself crushes gals in usage, but that only supports the contention, because girls is mainly used to describe female children.

In fact, if we NGram girls with boys (i.e., male children) we see that the usage is roughly comparable.

Most men don't appreciate being called "boys", but few women take offence at being called "girls".

"Guys and dolls" might be a step too far in the wrong direction, though.