If you manage to get homebrew back, make sure to turn off update checks and disable Wii Connect24 in Wii Settings so this doesn't happen again.Today at GDC 2009, Nintendo of America's Bill Trinen introduced the Wii SD Card Menu.
In addition to this frequently-requested functionality, the Wii can now handle SDHC cards up to at least 32GB in size (whether it can handle cards larger than 32GB has not been confirmed nor denied).It also expands the number of SD Card pages to 20, with 12 channel slots available on each page.In addition to these change to the local Wii menu, Nintendo has also updated the functionality of the Wii Shop Channel.Question: How Do I Restore the Homebrew Channel After I Accidentally Update My Wii?From time to time someone emails me to say their child or a friend updated their Wii operating system, resulting in the loss of the Homebrew Channel. Answer: An accidental upgrade is most likely to happen if someone plays a game that includes an update check and you haven't disabled Wii's update checking.
It can also happen if you have Wii Connect24 enabled, as this will automatically install any system updates released by Nintendo.
Updates 4.2 and 4.3 were both specifically designed to kill homebrew.
If you have lost homebrew but can still use your Wii, be happy about that, because sometimes the updates have made Wiis unusable. The latest upgrade as I write this is 4.3, but if you were updated by an older game you might wind up with 4.2 or even something older.
To find out what version of the operating system you have, go into Wii Options, click on "Wii Settings" and check the number on the upper right corner of that screen. Now you simply need to reinstall homebrew for the appropriate OS.
You can use my homebrew installation guide to learn how to determine which homebrew package you need and how to install it to your system.
Please note that I have not tried reinstalling homebrew onto a system from which it was deleted, so I can make no guarantees as to the result.