Not sure what you mean. This is a NUMBER field and accept only integer. 1 or 2 or 3 or ... 10 or ... 20, etc.
To remove the "slider", open the XML and find:
$form->add( new \IPS\Helpers\Form\Number( 'membersaway_days', \IPS\Member::loggedIn()->membersaway_days, FALSE, array( 'range' => TRUE, 'min' => 1, 'max' => \IPS\Settings::i()->membersAway_days, 'disabled' => $disabled ), NULL, NULL, \IPS\Member::loggedIn()->language()->addToStack('days') ) );
Change to:
$form->add( new \IPS\Helpers\Form\Number( 'membersaway_days', \IPS\Member::loggedIn()->membersaway_days, FALSE, array( 'min' => 1, 'max' => \IPS\Settings::i()->membersAway_days, 'disabled' => $disabled ), NULL, NULL, \IPS\Member::loggedIn()->language()->addToStack('days') ) );
To make the reason required, change this:
$form->add( new \IPS\Helpers\Form\Editor( 'membersaway_text', \IPS\Member::loggedIn()->membersaway_text, FALSE, array( 'app' => 'core', 'key' => 'Admin', 'autoSaveKey' => 'membersaway_text', 'attachIds' => NULL, 'minimize' => 'membersAway_text_placeholder' ) ) );
to this:
$form->add( new \IPS\Helpers\Form\Editor( 'membersaway_text', \IPS\Member::loggedIn()->membersaway_text, TRUE, array( 'app' => 'core', 'key' => 'Admin', 'autoSaveKey' => 'membersaway_text', 'attachIds' => NULL, 'minimize' => 'membersAway_text_placeholder' ) ) );
Reinstall.