Breakdown of Se tudo depender do tempo, talvez a gente viaje só amanhã.
Questions & Answers about Se tudo depender do tempo, talvez a gente viaje só amanhã.
Because this is a future condition: if everything depends on the weather in the sense of if it turns out to depend on the weather.
After se in this kind of future if clause, Portuguese normally uses the future subjunctive. For the verb depender, the ele/ela/você form of the future subjunctive is depender.
So here, depender is not the infinitive in function, even though it looks the same.