Not big fan of having conditionally registered event handlers as it makes analysis of the registered hooks harder and logic becomes more magical. We might consider introducing second parameter for `ElggPlugin::deactivate` that forces deactivation despite event output when facing fatal error on plugin boot. How about that?

Looks like we have only 2 cases when we should force deactivation:
- https://github.com/Elgg/Elgg/blob/master/engine/lib/plugins.php#L348
- https://github.com/Elgg/Elgg/blob/master/views/default/admin/plugins.php#L32