But being a super hero is not supposed to be a business or entrepreneurship. You're in it because you were bitten by a spider who had one too many bananas. If you want to become a brand, become a brand. Copyright, trademark, register your stuff. But that comes with the possibility of being outed.
Let's assume we live in the comic universe. Or more specifically, the comic universe lives in our universe. You can't tell me that every producer, director, publisher and cafe press store owner would not be all over these guys trying to get the trademarks to be able to licence their stuff or movies or books.
So if you're a hero, and you have a brand more power to you. Everyone that is a celebrity for whatever reason has a brand (I'm looking at you Jersey Shore). There's no reason why heroes with flashy costumes can't either.
I honestly think the heroes with enhanced powers should be immune to common colds and viruses. Spider Man, Capn America, Superman should never get sick. I would think Batman would have trained himself never to get sick.
Now for the guys who don't have that health factor or batman immune system, I would think it's about networking. You honestly need to have someone you trust that is in that position to take care of you if you do in fact get sick. And if you have to take a sick day, take a sick day. If you think that the city is not safe if you're not traipsing about it in your spandex, you have no clue. Sure being on patrol helps. But even cops can't stop all the crime.
Besides, Spider Man looks like a douche laying in the hospital bed like that.
How would any document be considered legal if it dealt with the probate of a masked hero? In most cases the world doesn't know your secret identity. So if they found Spider Man really dead. And "Spider Man" had a will, how can it be verified that it was really Spider Man that died. The public can only assume that it's the same person that has been under the mask from the get go. Which is not always the case since most heroes have had a stand in for them.
If there is no birth certificate of "Spider Man", there can be no official death certificate of "Spider Man" and I would assume no lawyer would be able to prove it was him the entire time. The only person that can really die is Peter Parker.
And who wants to leave a crappy apartment and take out boxes in their will?
I would also assume if the hero was competent enough to be able to keep his identity a secret the entire time, they'd have a contingency plan if they were killed. Why they heck would Tony Stark bequeath his armor to one of the thousands of kids he's likely fathered and pays their mothers to keep their traps shut? You'd have either the united states government vying for a piece of that technology or anyone else in the world (villain or wanna be hero) after that stuff real quick like.
So if you're a hero. Have someone you trust destroy everything. You don't save that crap.