All forms of investing involve risk, and sometimes, companies close up shop, file for bankruptcy, or get delisted from a public stock exchange.
However, in most cases, companies that undergo any of these scenarios may "restructure" as something else or are absorbed by another company, becoming a subsidiary of that company. The scenarios outlined below apply in the same way on every other investing platform or brokerage service as they do on Grifin.
If a company files for bankruptcy, their stock may become valueless, and investors might lose their entire investment. However, this is entirely case by case, and even the type of bankruptcy can affect how the company emerges from the bankruptcy and how it affects their shareholders. This article on FINRA's website helps explain exactly what happens in detail.
If a company gets delisted from a stock exchange, Grifin allows you to sell out of the stock, but you can no longer buy more of that stock. As a shareholder, you still own your shares in the company, but the stock will typically trade over-the-counter (called "OTC"). This means the shares may be harder to sell with lower liquidity and less transparency for investors, due to reduced access to the company's information since the company is no longer publicly listed. This article on NASDAQ's website helps explain this in more detail for you.
It's important to note that it is rare for a company to go entirely out of business. In most cases, the company will "re-organize" into something else, the stock price may significantly decrease, and then the company gets delisted. Or, the assets will get acquired by somebody else (like another private or publicly-traded company), and the stock may get converted to the acquiring company's stock.