Goodbye, a contraction of God-be-with-ye; adiós, with God: 'only ignorant Americans use "adiós" for anything less than forever' isn't what Ms. Leonard told Sam's freshman Spanish class, but it's certainly what she meant, or near enough. Salt and fire like Bobby wants would be 'adiós, Dean', sending him off with a God that Dean never believed in and Sam knows is neither with Dean (that's the point of hell) nor answering Sam's voicemail (six days covering the fourteen billion years between the Big Bang and Adam, and on the seventh day, God rested).
Sam tends Dean's body with the same care he'd use were Dean alive (the less he has to do later to repair the damage, the better), makes sure there's a lighter and a knife in Dean's jeans pockets (he'll wake up in the dark, and he hates being weaponless), buys thin plywood from Lowe's and builds a box, digs a hole the depth of the box plus six inches (can't be sure of being there when he wakes up, can't let him suffocate before he gets out); hasta pronto, Dean: see you soon.