Faking your death is not illegal in most jurisdictions, nor is it fraud in and of itself.
Also, you could well argue that this case is very much outside of the intent of the law as written, which takes death to be a permanent, irremediable state - and that's true for, well, pretty much everyone EXCEPT Mr. Immortal (and maybe some other superheroes, who knows). That doesn't automatically mean the law will treat him differently than every other person; in fact, as per most legal doctrines, it HAS TO treat him the same as everyone else.
There's tons of everyday concepts enshrined in law that could, in principle, fall to pieces once you break the assumed rules of nature. "Legal person" for example, would break itself against someone with the power to copy himself at will, making it impossible to discern who was/is the original and whether there even IS such a thing as "the original". And so on.
You could well argue - and Mr. Immortal actually does in the show - that he absolutely "dies"; it just doesn't last forever. You have no proof that other deaths last forever, either, by the way. We just have never seen it not last forever, and all we know about the universe SUGGESTS it lasts forever; but e.g. religions might disagree. So that's not even necessarily a legal defense, since when you throw out established natural order, the permanence of other deaths might not be provable, either. In which case a "temporary" death such as Mr. Immortal's would have to be treated the same as other deaths, which might be as impermanent, just over longer time scales. Not to mention what could happen with resurrections - are the people who got blipped in the MCU not also victims of "temporary death", for example? Theirs lasted a few years, Mr. Immortal's lasted a few seconds (or minutes or however long) - a difference that the law doesn't necessarily have to care about as it is written.
Most definitions of death in a legal sense rest on "common medical consensus". They also employ language about "irreversible" states, however historically we've found that this doesn't hold - as medical technology improves, previously irreversible states can in fact become reversible. And since we KNOW that resurrection even on a planetary scale is a thing (Blip and all) that's not exactly a solid leg to stand on. Which means Mr. Immortal could simply argue that as long as he kills himself in a way that under "common medical consensus" would constitute undisputable "death", the fact that he alone happens to survive it would not allow the law, as written, to apply differently to him.
It would be something that would need to be argued in court, of course, and there are possible counterarguments (such as e.g. him knowing it won't actually cause irreversible cessation of life). But it's not like it's clear-cut by any means. And it would likely require a revision of extant law to account for super-powered individuals.
That's a different show entirely, though