Here’s a quick plugin to block or unblock all web users based on how many days since they logged in :
Plugin General =>
$pre = $modx->db->config['table_prefix'];
$today = time();
$diff = ($days*24*60*60);
$cutoff = ($today-$diff) ;
$result = $modx->db->query( 'UPDATE `'.$pre.'web_user_attributes` SET blocked= '.$block.' WHERE thislogin < '.$cutoff.'');
Plugin Configuration =>
&days=Days;list;5,10,20,30,60,90,120;30 &block=Block;list;0,1;0
Then choose the number of days and set block to 1 ( 0 = unblock)
Plugin System Events =>
OnManagerLogout