For a company to "exist" in Canada he'll need a business license, some kind of WCB coverage (workers compensation board - a general disability policy publicly managed by the province they live in) and a GST number. Once he has these things, the company legally exists. And he'd need all of them in order to file taxes showing that he owned a company. I've done all this myself to set up my own sole-proprietorship company in BC.
So, if he's filing taxes the company, as a legal entity, exists.
If you want it to be some kind of shell company or front, that's a different statement.
If you want the company to be basically a money laundering operation for demon-generated revenue, what's stopping this company from actually existing? It can still have an office, a receptionist, an on-staff bookkeeper, etc. 3 to 5 employees in a light industrial park or trendy but sort of rundown downtown neighbourhood (those are almost always leased by the way, unless he owns the whole building and is renting out the rest of it). The complexity of actually having a legal company, with employees etc. seems a little more like there'd be some amount of mystery invovled in the finding out of revenue sources. The guy himself could make up the "clients", and being that he's the owner and only sales person, and all business activities take place elsewhere, there's no reason for any of the employees to question what kind of "consulting" he does....
If you want realism, you can't just oversimplify to the point of "the company doesn't really exist" and expect intelligent readers to buy it.
Also, I'm not sure about joint bank accounts not being frozen after a death. Assets like houses and cars would remain in her posession during probate, but joint accounts may not. Any accounts holding company money, since the company is in his name, would also be frozen during probate, regardless of who he was leaving it to. The executor of the estate may be able to access a small portion (since the executor gets a portion anyway) but unless the cash is in her name entirely, she's going to be broke for at least 6 months, up to 2 years, while the will is executed. My grandmother's estate was a handwritten will with only cash assets, and a small house, (easiest kind to deal with) and no one contesting anything, and it still took more than 6 months. A friend waited a year and a half for her inheritence from her father, a mechanic who rented in a trailer park.