for example it's cause error in mantistouch:
8: Undefined property: stdClass::$name
File: /home/support/domains/m.support.overmind/public_html/views/issue.phtml
Line: 81

But i think it's better if we handle it in the API:
soap/mc_account_api.php

patch:
if( user_exists( $p_user_id ) ) {
.......
}
else {
$t_result['name'] = lang_get( 'prefix_for_deleted_users' ) . (int) $p_user_id;
}