yeah somehow the varden will get the egg whether eragon and saphira steal it or thorn and murtagh turn good and steal it. its possible roran will get it but i think elva will get it. it seems she is too young but remember she grows fast. also she is destined for a life of more than a normal person because of eragons blessing and saphiras gift. if elva did beocome the new rider, she could use her gift to kill galbatorix. she is the ultimate weapon. another possibility is that vanir could become the new rider. from what he says in ellesmera, it foreshadows that he or an elf may get the egg to hatch. it could also be one of the elf children because in brisingr, they are unique. roran will eventually be able to lift the rock and eragon will tutor him in magic. i think as deadwing said the last battle w/ galbatorix will take place in the hadarac desert and saphira and eragon will flee to Du Fells Nangoroth. for those who dont know it is the mountains in the middle of the hadarac desert where wild dragons used to go to mate, raise their young, and eventually die. since they all go to die there it is most likely that eragon and saphira will find many more Eldunari which eragon will use to destroy galbatorix.
another way could be that eragon will find the answer to destroy galbatorix in the Dominance of Fate, the book Jeod gave to him. or like oromis said, they must simply find the spell to kill galbatorix that he overlooked. it would be fitting that this would be brisingr, galbatorix probably has a spell to prevent spells from killing him. however eragons sword is unique and can be used to kill him. it would be ironic because while chasing the razac, urgals, under galbatorixes orders destroy yazuac where eragon first uses magic, brisingr through his bow.
this may not be, these are just my predictions but whoever gets control of that dragon egg whether its the varden of the king, will control the fate of what happens.
whats cooking good looking?