Archaic or highly formal parting word; in modern Japanese it sounds theatrical, literary, or old-fashioned. Not used in everyday conversation.
Farewell, my friend.
Dated conjunction used in formal or written contexts; equivalent to modern それなら or だったら. Often seen in older literature or formal arguments.
If so, let's do this.
だったら is a casual, conversational equivalent for 'if that's the case', while さらば as a conjunction is stiff, archaic, and rarely heard in speech.
Standard kana spelling; the kanji form 然らば is rare and mostly historical.
Rare kanji form; learners will almost always encounter the kana spelling.
Derived from classical Japanese 然らば (さらば), originally a conditional form of 然り (さり, 'to be so'). The interjection use developed from the conjunction sense.