Try modifying that block like this:
RewriteCond %{HTTP_USER_AGENT} "Somebot|Otherbot" [NC,OR]
RewriteCond %{HTTP_USER_AGENT} "Anotherbot" [NC]
RewriteCond %{REQUEST_URI} !(/mypages|/otherpages) [NC]
RewriteCond %{REQUEST_URI} !index\.html
RewriteRule ^(.*)$ index.html? [R=301,L]