Player death is always possible, yes. Wouldn't be a real war if it wasn't. However, like Kaz said, player death in the 1st battle is a slim possibility. I trust in everyone's personal skill to see them through to the end. I also plan to have several suprises thrown into player fights to help even the playing field when needed. Keep in mind, as GM, i not only control the NPC's, but i also control the environment around you. All the ships, all the NPC cannon fire, even the ocean and the sky are under my command. Suffice to say, i plan to keep this interesting and entertaining.
If you die, then yes your character is out. However, you are not barred from making a new character, even on a different faction if you wanted. However, whatever new characters you make will not be eligible to participate in the same battle that your original character died in. Can't die, then make a new character and inject them into the same scene where your other character died to continue the fight.