You are able to join a raid as long as you have stamina.
Scenarios:
- When you join a raid at 200 stamina, it will deplete your stamina to 0.
- You are still able to join raids at less than 200 stamina
- For example, you join the raid at 100 stamina but this will drop your stamina below 0.
- In reality, the character stamina is -100, but it is showing as 0 in the UI
- The stamina of the character will remain at 0 for some time until the lost 100 stamina is recovered