Throwing a sword is no different that throwing a chair, an enraged badger or a beer stein. Improvised thrown weapon, DEX vs AC, no proficiency bonus, range 5/10, 1d4+DEX damage. A kind GM would allow the sword's magical enhancement and properties to apply.
If the character is going to do this regularly, you might allow "weapon proficiency: improvised" or a "throw anything" feat to allow a +2.
Regarding using STR instead of DEX for some large thrown objects, trating them as Heavy Thrown improvised weapons, that would be a house rule but I see nothing wrong with it. If you do so, it would be reasonable to treat all two handed or versatile weapons as Heavy Thrown Improvised.
Magical throwing weapons return to hand after thrown, but I don't know that someone enchanting a longsword or halberd would bother including auto-return in the magic. Maybe this is one of the few cases where a swordmage's swordbond actually makes a difference.