Archaic concessive expression meaning 'even if that is the case' or 'nevertheless'. Found in classical Japanese texts; not used in modern speech.
Be that as it may, one should choose that path.
Classical Japanese phrase composed of 然 (さ, 'so') + こそ (emphatic particle) + 言え (已然形 of 言う, 'say'). Literally 'even if one says so'.