Learn Spanish (Latin America): Aunque rompan el pacto, el cual es importante, hay que continuar. - Even if they break the pact, which is important, we must continue.

While you could use que, el cual is a slightly more formal relative pronoun often used after commas to add extra, non-essential information about a noun. It translates to "which" and must agree in gender and number with the noun it refers back to—in this case, the masculine singular el pacto.

Could I use the neuter lo cual instead of el cual in this sentence?

Not without changing the meaning! El cual refers specifically to the noun right before it, meaning the pact itself is important. If you used the neuter lo cual, it wouldn't refer to a specific noun; it would refer to the entire preceding idea, meaning "the fact that they might break the pact is important."

Why is the verb romper in the subjunctive form (rompan)?

The word aunque takes the subjunctive when talking about a hypothetical situation or an unconfirmed future possibility. Because the English translation says "Even if they break" rather than "Even though they are breaking," it is treated as a possibility, requiring the subjunctive rompan.

The translation says "we must continue", but isn't hay que impersonal?