These days it's totally fine. A lot of motherboards actually have several ways of dealing with this. One of the ways is the flashing is done in a separate part of the memory and the pointer is only updated if the write worked and is checksum verified. Another way of dealing with it is dual bios where there's actually two versions of the bios you can switch between (or is switched automatically). A third way is a recovery mode, where you can flash from a USB drive in a specific port even if the normal bios is totally corrupt.

Even back in the days it was mostly fine. You could just order a new bios chip from the manufacturer. Or if you had access to a programming device, you could take the bios chip out of its socket and program it outside the computer. Back in the old days many computer repair shops offered this as a service. If you had another computer / motherboard with a similar bios chip you could often hotswap the chip and flash it like that. A little bit risky, but works in a pinch, I've done it before.

But the process was annoying, where flashing would take a while and the flashing software maybe wasn't the best. So if it would crash or power got interrupted, you could be stuck with a non functioning computer. Lots of ways to fix it, but for a regular person it could mean not having a computer for at least a few days.