RewriteEngine On

# Match requests like /?node_id=12345
RewriteCond %{REQUEST_URI} ^/$
RewriteCond %{QUERY_STRING} ^node_id=([0-9]+)$

# Skip if the cookie header contains userpass=
RewriteCond %{HTTP_COOKIE} !(^|;\s*)userpass=

# Serve cached file if it exists
RewriteCond %{DOCUMENT_ROOT}/cache/%1.html -f
RewriteRule ^$ /cache/%1.html [L]