On more than one occasion I have found my party right before a boss fight, at the heart of a fast-travel-denied area, and sometimes I can't even leave the place e.g.
Inside the Astral Prism.
Without knowledge of that, I'm often not in great shape to tackle the fight. I've only succeeded by cheesing or luckily finding an Angelic Slumber potion.
Is there a way to fully restore the party in those situations (assuming I don't have the right spells and consumables), or do I need to load an older save file?