For instance: boyfriend invested a lot and managed to secure them (they never devalued as he kept them stable for a while) but one day he passed away, the thing is that he is the main shareholder who owns said corporate entity when he was still alive (so he's the only signatory noted on paper) so what happens then? Most of the legal framework and bureaucracy are all under his name.

It definitely won't his girlfriend who'll taking over as it's not even under her name nor was she delegated that responsibility prior as the title and experience of shareholding is under her boyfriend's name. I mean, shareholders are human beings (corporations are formed by people). In this case, he is the founder of the company that managed to take off financially that succeeded.