By default, if your shell crashes (Explorer.exe), it will automatically restart. If your shell crashes (icons/Taskbar disappear) and your must logoff/logon to restore them, edit the following Registry entry:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon

Look at AutoRestartShell (a REG_DWORD) in the right hand pane. If it is 0 (do not restart), set it to 1(automatically restart).