I dont know what site management software your hosting company uses, if any, but in apache there are ways to create redirects, where if a url is entered for the domain, ie, www.domain.com/event/index.html it could redirect it automatically to a different page, IE, www.domain.com/event.html
You could also edit the htaccess file and create custom error pages, which could in turn redirect someone, but the 404 page would be the same, and hence, redirect to the same place, no matter where on the domain generated the 404.
You will probably need assess to the site regardless to do any of this.