If index.html will no longer exist ... YES, but redirecting to just directory/ would probably be better, and more consistentwith inbound links, if page.hml is just going to be the new directories default page. Have a read of SEO advice: url canonicalization in Matt Cutts blog http://www.mattcutts.com/blog/seo-advice-url-canonicalization/ It should help
If you rename the page.html to index.html and put it under a drectory like /page and redirect the index.html in the root to /page it would be nice for SEO. Redirecting to a directory or subdomain instead of a page url is better