I'd imagine the same as ours: broadly speaking, random shit that just happened to show up one day. They'd just need fewer of them than we happen to use in English.

Pronouns as a word category aren't as inherently linked to gender as you'd think, just commonly influenced by it. You're presumably asking from an English viewpoint, where we happen to split some third person pronouns by gender. Finnish, for example, already doesn't do that, their only equivalent of he/she/they is hän which, like "they", goes for anything. Japanese has absolute shit tons of pronouns of all kinds, some of which are very gender linked and some of which are fairly equal opportunity.

The connection between gender gender and grammatical "gender" is kind of overrated anyway, speaking as a native of a language with gendered nouns. The name is misleading: people obviously have genders, but when generalized to all nouns it gets... arbitrary as hell. Practically it's just an extra bit of information you need to memorize for each one. What would it even mean for a book to have a gender, and why is it what it is? (The answer is unfortunately "fuck you, that's why" because natural languages aren't required to make any logical sense)

On the upside, if you're German you can make your news headlines real short and awkward to read. It's like code golf, or something.