Windows Explorer crashes sometimes and it is supposed to come back up automatically. Did yours do so?
the real answer is that explorer is just a shell and you can tell windows to use just about any program as the shell, even calc.exe, though you wouldn't want to because you wouldn't be able to open any files! (Well, you easily could by hitting CTRL-Shift-Esc and choosing file->new task)
you can change to a custom interface by START-> RUN -> GPEDIT.msc (that is, Group Policy Edit)
then, find User Configuration -> Administrative Templates-> system and in the right window double-click custom user interface
If you enable that and choose an .exe, that other .exe will start instead of explorer.exe
For example, I just now changed my shell to cmd.exe and rebooted. Instead of the usual windows explorer, I see my command window and nothing else. No start button. no tray full of icons.
So, sure, you can get rid of Explorer. There are dozens of high quality alternatives to windows explorer out there that you can download . Lifehacker has a good article about one of them:
http://lifehacker.com/software/geek-to-live/replace-windows-explorer-with-xplorer2-258730.php
and here is a bigger list:
http://www.simplehelp.net/2006/10/11/10-windows-explorer-alternatives-compared-and-reviewed/