Help with 400ex, broke exaust stud

Well, we had a rattle coming from somewhere on our 400ex, and we had the hardest time trying to find it. The other day I was just cruising and I bend over to look while riding and I spot the exaust collar thing is loose. You know the collar that goes around the header to keep the header tight to the head. Well so we try tightening the nuts, nothing, probably rusted tight. So we try loosening um too. Well of course they start to move, and finnaly just the nut and tip of the stud just twist right off.

What is the reccomended procedure for backing out that broken, and probably extrememly rusted stud? And what caused the collar to get loose if the nuts were night? Is this one of those stud pulling out like on the head type deals?

For extraction should the head be taken off to work on, or just leave it on and try and take it off from there? We're thinking of stripping the bike down and sending it to the dealer to do. By stripping it we'd save them the hours ($$$ for us), and we don't have the experiance to be messing with the expensive parts like the head. How hard is it to take the head completely off of the motor?
Thanks.