Okay, so good news and bad news.
Good news is, I found out a way to get to the Heroic Ending.
Bad news? It does not work - at least if you're dating Sarah. I can't vouch for other characters.
Do the Heroic route as usual but NEVER grab Ashley. Yes, I'm serious. You may not grab her.
When confronting Julia, push past her and beat her dungeon.
Once done, do NOT speak to Dr. Tiff. Instead, head home and meet Julia.
Wait in the library for all scenes to complete (the last one involves a monster appearing in the library). Once done, head around town.
I recommend going to the protagonist's house first so you can heal (also unlocks Val). Next is up to you, but I prefer this order:
Head to the dungeon (1st floor) to get Sarah.
Head to the Item Shop to get Molly and Derrick
Head to the Town Square to get Kate - Enchantment Shop to unlock Brittany's enchantments again if you don't have them already.
Head to the Lake to get Reese
Head to Drape's room to get Cassandra
Next, reach floor 24 to fight a (rather tough) boss fight. Once done, head out and head to floor 25 (floor 24 sigil doesn't work). Head to the depths of that floor (hint: take the right path) for another boss fight. Again, this one is bugged so one of the options doesn't work. So you'll have to beat it.
Head out and speak to Angie in the square. Choose any option when prompted.
Head back to the school and lose the battle. Watch a scene and... yeah, Val's in the hallway but you can't click on her.