When you suffer Ability Score loss, but survive, roll on the appropriate table for the Ability Score that you lost points in. Common sense determines if they're permanent or temporary. If unsure, it's 50/50.
STRENGTH (from physical attacks)
1: Gushing wound. Lose a further 1d6 STR every turn until patched up.
2: Maimed. Roll 1d6 and lose 1: Head, 2: Hand, 3: Arm, 4: Leg, 5: Ear, 6: Eye.
3: Spinal Tear. Any STR loss from this attack is permanent.
4: Whatever caused the harm is lodged inside you. It causes another 1d6 STR loss if it's not pulled out carefully.
5: Punctured Lung. You wheeze loudly forever.
6: Brain Hit Bad. Lose 1d6 WIL permanently.
7: Concussion. You act like a dope for the rest of the day.
8: Ruined Arm. You cannot use a random arm for anything. If you lose your good arm, attacks with your off-hand are Impaired until you get used to it in d20 Months.
9: Broken jaw. You can't talk properly until it heals.
10: Crushed ribs. If you take further STR loss before your next Full Rest, you take an additional 1d6 damage.
11: Choked. You can't breath without assistance, and will die in 1d6 turns unless somebody helps you.
12: Flesh Wound. It's not all that bad. Wicked scar too.
STRENGTH (from other sources)
1: You throw up a lot.
2: You have the shivers at the slightest cold.
3: Foaming mouth.
4: Lose clumps of hair.
5: Your complexion goes all gross and yellow.
6: Bad reaction! The STR loss is permanent!
7: You become so sickly that you can never regain lost STR.
8: One eye dies.
9: Half of your face falls immobile.
10: Hair turns grey/white/to-dust.
12: You shake it off! ARGH!! RARRR! I'M HARDCORE.
1: You've got the shakes forever. Lose 1d6 DEX to a minimum of 1.
2: You'll never dance again.
3: You can't stand up quickly anymore.
4: Spasms whenever least convenient, unless you pass a WIL Save.
5: Cannot walk at all without a stick.
6: Hobble for the rest of your life.
7: Comatose. Attempt a WIL Save after d20 days to restore movement.
8: Balance is shot. Require DEX Saves for things that aren't even difficult ordinarily.
9: You can't turn your neck anymore.
10: One eye permanently closed.
11: Slack tongue. You sound like an idiot.
12: You drool if you're not careful.
2: You need a drink to steady your nerves, otherwise you have the shakes.
3: You have a phobia of whatever did this to you. WIL Save to confront it again.
4: Surge of idiotic heroism. You can only act if it's suitably stupid and heroic, until you get a short rest.
5: You become an incredibly picky eater. WIL Save to avoid vomiting any meal.
6: Insomnia. You only benefit from Full Rests if you pass a WIL save and get some sleep.
7: Sensitivity. Sudden, loud noises cause you to lose 1d6 WIL.
8: Delusion. From now on the Referee rolls all your dice and keeps track of your scores, damage etc. in secret.
9: Obsession. You cannot benefit from Long Rests until you confront whatever did this to you and get revenge.
10: Anxiety. You cannot benefit from rests until you're somewhere completely, 100% safe, and not even slightly dangerous.
11: Trigger Happy. Whenever there's a surprise, and you're armed, you must pass a WIL Save to avoid attacking the surprising thing.
12: Hallucinations, only when you're alone, and you can only find out if they're real by touching them.