Yeah,
I have no idea what diploma you're talking about as I'm not a Krav guy. But, if it's a certificate that lables him as an "instructor" they could have a valid argument for not giving it to him. Just because you can DO doesn't necessarily mean you can TEACH and pass it on properly.
So, if say he left on the note of something like, "screw you I'm going to go open my own school and do it the way I want to!" Then, no, he gets nothing along the lines of help from the school and teachers he has forsaken.
If you say it was on good terms that he left and then there's another possibility. (again remember always that I'm assuming this is some kind of instructor qualification) It takes a whole lot more knowledge of small details and applicatoin and theory to be an instructor than to be a non teaching MAist. We get our 'Instructor certificate' around 5 to as much as 10 years in FROM 1st DAN BLack Belt. And you would never pass those tests without years of learning HOW to teach.
Bottom line, I could see many reasons why someone would be denied just about anything from a school he abbandoned. If it's not that, then there's a simple fix... go teach for that school until you earn your cert. One piece of instruction I got years ago from one of our Masters was: "You always have exaclty 2 choices: Yes Sir! or No sir, I'm sorry I can't do that. I will be leaving now... and leave with a proper bow/salute etc. This way, you leave with respect for all parties concerned. But, you still have LEFT. YOU WALKED AWAY. You can expect courtesy and general respect from your former instructors/classmates. But you should never assume that they OWE it to you to help you start up a school accross the street that will directly compete with them. ( or anything along those lines )
C'mon people! This ain't piano lessons! And it's not whine tasting either, so eat your cheese, swallow the Whine, and walk away TALL.
Deep breaths. Ok. I'm better now. Sorry, that's just a touchy subject with me.
Maybe I'm just funny that way. Respect and honor those above you. Respect those training with you. And love those training under you. If you're friend can honestly say that he's done and is doing those things, then maybe I'm 100% off the mark here. If so, I apologize respectfully.