you need to go way ahead of the zeppelin and ignore them calling you back, as mentioned use the nuke on the big islands every time it reloads and take out the ballistas while waiting for it to power up.
If you are getting killed a lot you can go to the settings and set the game to auto pause when your health gets to a certain point. then use your heal spell and or potions, also don't forget to use your flying buddy to take some of the damage awary from you.
I will admit escort missions are not my favorite things to do (need to ban these things )but good luck and keep trying you will win in the end!!!!
