In that case, event receiver still attached to the list and cause alot of problem to your site.Only thing you can do is simply delete it.
run this script to get the event receiver attach to a list.
$spWeb = Get-SPWeb -Identity http://web.spdev.local
$spList = $spWeb.Lists["My List Name"]
$spList.EventReceivers | Select Name,Assembly,Type
Now you want to delete it.
$spWeb = Get-SPWeb -Identity http://web.spdev.local
$spList = $spWeb.Lists["My List Name"]
$eventsCount = $spList.EventReceivers.Count
$assembly = "Project.Name.Class, Version=1.0.0.0, Culture=neutral, PublicKeyToken=24242342424"
$class = "Namespace.MyClass.ClassName"
$type = 10002
$name = "My Event Name"
for ($i = 0; $i -lt $eventsCount; $i+=1)
{
if ($spList.EventReceivers[$i].Assembly -eq $assembly -and
$spList.EventReceivers[$i].Class -eq $class -and
$spList.EventReceivers[$i].Type -eq $type -and
$spList.EventReceivers[$i].Name -eq $Name)
{
$spList.EventReceivers[$i].Delete()
}
}
$spList.Update()
http://blogs.solidq.com/sharepoint/Post.aspx?ID=80
Also check this post as well
http://naimmurati.wordpress.com/2012/03/22/add-modify-or-delete-list-event-receivers-with-powershell/