The things that happen in the world you create have to make sense. Maybe not to the players, but you have to understand why things happen and what the likely repercussions of your players actions are.
You can change things after the time as long as you’re careful. I generally work to the following rules in most cases:
- Death should be final - even if you made a mistake. Once players are dead they are dead. Unless you had a built in mechanism that all players knew about it’s not worth the damage that undoing death will do. If necessary, admit you made a mistake, but apologise and move on.
- Acknowledge your players actions. There should be results for their actions. They don’t have to be the results that they wanted, but acknowledge their effort.
- It’s your game. Decide what’s important to you, lay it out clearly and stick to it. Accommodate players ideas, but within your structure. It helps you to stay keen, and it helps the game to have an identity. It’s fine to say no to people.