if u can install bootmii as boot2, yes, u will be able to recover. If u cannot install bootmii as boot2, but only as IOS, having a nand backup means you can recover from any brick using an infectus modchip, but its a complicated process and I would recommend just mailing the wii to [email protected]
if you ever encounter that situation (it will cost less than actually buying an infectus anyways, and infectus are hard to find now too). However, if u happen to have priiloader installed and a nand backup, u should be able to recover from most bricks without having to use an infectus (as long as u don't screw up your system menu or system menu IOS).
But basically, if u use either of the stickied guides on this forum, u should be very safe. As long as u follow the instructions exactly, the only risk u face would be losing power during the installation of a vital file (ie. system menu, system menu IOS, or priiloader)... so all in all, as long as u follow a good guide, it is VERY safe.
And once u complete the softmod, and have a nand backup and priiloader installed, u are VERY safe as long as u don't uninstall or stub your system menu IOS or system menu.