I saw some good advice on the other thread as to good hardcore run tips and strategy (props to @Satsukiye_ specifically, really helped me.) I was nervous using Total Mess because of the guides I had read that said it would cause you to drop your main weapon (if I spent the whole game trying to make the chainsword, I don't want it to be discarded 3 turns later.)
I found that, atleast on the PS4 version, while the Total Mess perk can cause you to drop the weapon you have equipped from your bag, the weapon will remain equipped in the upper right hand corner and in fights. So I would keep playing the first 10 levels until I found the old man, quit to menu and go back in until he had an endgame weapon for something I had on hand (or could easily get like scrap metal or tape,) and then equip it. Even when I dropped the weapon 5 floors later, I would still have it equipped for the remainder of the game.
The only catch is that you can't switch weapons (because you don't have the weapon in your bag to switch back) or go to the menu because when you log back in you will lose the equipped weapon.