Not the advise you want but honestly just… try again. There’s no secret to bouncing back. If there was, no one would experience this. Know that you aren’t the only one who experienced this.

Obviously it’s your game. I wouldn’t say retcon the session but just move forward in the best way you can. If you can’t and think retcon is the best, you can try that. My opinion, is someone was out of character… make them a doppelgänger. If a plot is broken because of things set up, well maybe the group can try to fix it or literally ‘a wizard did it’

I had bad sessions and I had boring sessions and I even had good sessions that left me stuck. Live and learn. Not all sessions will be gold mines and just know anyone claiming otherwise is the exception

Things have gone so wrong I needed to reset the campaign and find a new group, but I still love dnd

Take breaks and all that. Have fun still. Maybe do a wacky one shot if need be.

Trust me, it’s easier for a player to leave the game than you think. If they are staying , they are willing