setnpcinvincible

not available yet. need to use editnpc GUI to enable

Unfortuntely there is no direct console command for that... but there are basically two alternative ways to make npcs invincible

1. Either use the generic edit command while looking at the npc: just type edit attribute invincible to toggle the invincible attribute
2. Or use the editnpc command to bring up the npc edit menu, as mentioned by Juggernaut , then tick the "Invincible" box at the bottom