If we 'missed' the bus then it happened in the past. ' If the action happened in the past it makes things more tricky as you're talking about 'if' something happens which has already happened (or not)! 'If we (had) missed the bus, we would have taken a taxi' sounds natural to me if you're looking at the past tense and a hypothetical event.
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Kelly TanIf we missed the bus, ...You need one of these: