Oh, I knew I forgot to dd something. Generally if I can get in contact with the player, I ask if they want that character to be killed, disappear or NPCed and let them decide. If I have no way of knowing, I tend to let them fade into the background.
My personal advice as someone who DMS a lot offsite, Very first thing before anything else: DM the player. Sometimes inactive players aren't inactive because they don't care about the roleplay or the plot or their characters, sometimes, the alerts don't go through and they didn't even realized...