This game has a dynamic campaign, you will never see the exact same campaign mission twice. That said, if you die in campaign mode that pilot is done, period. Since you are new to the game I would suggest you fly quick flights or scenarios, they have a button that says pilot never dies. The scenarios can be quite difficult, but they are the same mission over and over, you will have to enlist a pilot in the appropriate service, ie, British, French, Belgian, German, or US, to fly that service's planes for those scenarios. Quick flights are the same way, you can pick your service, plane, and simple scenarios, and you will see the same mission over if you wish to try it again (just press go to field when you get back to the screen). Just make sure you have clicked pilot never dies. Also if you opt for an air start (not field in the altitude box) you will need to throttle up immediately (even if you joystick has the throttle set on full) pull the throttle back and advance it, the game will not recognize the previous throttle input.
Try those things first, so you can get familiar with the flight models, then try the campaign mode, don't be discouraged. It is very good immersive game and personally I have been flying it for years and have never lasted a year (in game time). I have only completed two campaigns, and that was because the squadron was withdrawn from the front.
Have fun!!
Mike