The new URLs are structured as follows.
index.php?option=com_comprofiler&view=userprofile&user=USER_ID
All of our API calls will output profile URLs like this. The only reason for your URLs to still have "task" is possibly due to hardcoded URLs in HTML or those from external sources. Even menu items can be updated by simply editing them, selecting the profile CB menu type, and saving the menu item.
As for search engines they'll propagate the changes once the bot goes through your site again (pretty often for Google, but you can force this from Googles webmaster console). I believe you can also supply a root file to let Google know what URLs have changed via a sitemap.
Both task and view work though so your already existing search propagation will continue to function. So I don't fully understand your need to rewrite the URLs. If SEF is enabled then our router.php will already handle rewriting the task to view for you.
Sorry, I've little experience with htaccess rewrite rules. I suggest checking the htaccess documentation below.
httpd.apache.org/docs/2.0/mod/mod_rewrite.html#RewriteRule