This is unlikely. When a registrar goes bust, the registry can take over, assign a replacement registrar by buyout or alternate agreement. See “Registerfly” case as an example.
In some cases though, the registrar only pays the registry for 1 year at a time, making the money their customers pre-pay effectively a low-interest loan for the registrar. If that registrar goes bust, you'll be able to transfer your domain to a different registrar, but you'll lose the money you paid (i.e. loaned) to the original registrar.
There's also another risk: if you decide after 2 years you're not happy with your registrar, tough luck, you've already paid for 10 years.
That's not usually a problem. You can transfer a registration with N years remaining, the new company will charge a one year registration and you now have N+1 years covered.
The only time it becomes a problem is if your new registrar doesn't support N+1 year registration - your 8-year example means you need to find someplace that supports 9- or 10-year regs.
Read the first part of my comment again. Some (many?) registrars don't actually register the domain for N years at once with the registry, even if you pay them for N years.
If they don't pay the registry, wouldn't it not show up in whois? If it doesn't show up with the expected expiration date in whois shortly after registration/renewal, I'd be demanding it get fixed.
There's also another risk: if you decide after 2 years you're not happy with your registrar, tough luck, you've already paid for 10 years.