I’m not sure where in my suggestions I said to deactivate the plugins (because they aren’t there and there’s no admin area), switching themes (no themes and again no admin area), or resetting the plugins (again, plugins aren’t there). At least what I’ve suggested didn’t involve 3 out of 4 steps that are just plain impossible and wasn’t just a copy-and-pasted response that’s been used before many times. I’m sorry if I offended you by pointing out these errors.
I would hope that my suggestion will help. As you said most good hosting companies can help out like this. If they can’t in this case they’re in trouble because I’ll bet that there’s no backups anywhere else. If there’s no backups, there’s very little chance of restoring the site to what it was before unless you’re using unmodified versions of every plugins and a completely unmodified version of the theme.
If we’re lucky and everything was just out-of-the-box and unmodified, re-installing the core WP files and re-installing the theme may work – BUT seeing as how this was done via Fantastico, you will create a bit of havoc if the version of WordPress doesn’t match the version that fantastico uses (Hint: It almost never does because fantastico is behind in what it uses most times). As a result of all of this asking the host if they can restore a backup that they have is really the best option in a case like this. If they can’t do that then we’d have to look at other much harder options, but until then we can hope that it’s a god hosting company.