OK, I am not 100% sure how this works but if your only gladiator is killed and you don't have the gold to have him resurrected or buy another slave it looks to me like you are going to have to start over of buy a bunch of trophies and sell them for gold. My fighter was killed last night and luckily I had the gold to bring him back but if he is knocked out again before I make more gold, I am out. I would highly suggest that all new managers upgrade their barracks as soon as you can so you can so you have more fighters and bring in more gold so it becomes much more unlikely that you could get in this mess. Also, it would be a good idea to always keep over 300 gold in your vault tell you have several fighters.