Oh, boy! A couple of lessons to be learned from recent web experiences:
1) Keep a mirror image of your web site at all times. If money is an issue, mirror it or a basic, no-frills subset of it, at one of the free web site hosting places like www.netfirms.com. Arrange for a redirection of the domain name through www.mydomain.com. This should minimize the down time, maybe even eliminate it. At least be equipped with a meaningful message for your visitors to inform them that the site is down or whatever.
2) Maintain an email address somewhere else too, like yahoo or hotmail, not just at the web site. Otherwise, if the web site is down, you will be unreachable. Capture the email received through your web site (and its mirror site) through email forms and route it to one or another actual email address. This will also minimize the potential for spamming. Simple and free email forms for redirection can be set up at www.bravenet.com. It's easy to change the email address to which these redirect with a simple click.