I'll try to help with as little spoilers as possible.
1) You can kill the gobos. If you have a level 3 or better still level 4 party it is doable.
2) There are many other access points to the Underdark that will allow you to get where you want to go or even access the goblin camp interior
3) If you play again or load an older save, take a closer look at the door in Gut's chamber before fast traveling out. You will find another fast travel waypoint a little ways in.
