Undead pets are a little lack luster. Their damage and health is far below other tames, despite the more difficult process to obtain them.
A solution would be that when Undead Pets die, they respawn either at their location of death, or respawn at their last “guard” location like scouting. The respawn timer could be 3-5 minutes to reassemble.
This allows undead to keep its true necromancy feel, while giving them a Niche use for Base defense or just throw away creatures your not worried if they die as they will come back.