I think the difference lies in whether anyone who knew the deceased remain among the living.
 
However, in a magical world where some being can live for millennia and others can become animate again after death, then that line can often become much blurrier than it already is in our real world.

A grave-robber is here for loot and doesn’t care what they end up destroying in that pursuit. Archaeologist is here for knowledge which they wish to share with the word while taking as much care as possible to preserve history. Also these days archaeologists need permission.
 
In fairness, their didn’t used to be much of a difference.

When it is the only way anyone will ever remember not just the entombed, but the society who entombed them.
 
Of course, immortal sphinxes complicate that answer.

Hope there is a part 2 hehe

Grave robbing is for personal gain. Archeology is for historical knowledge.

I would say a couple of thousand years

When the tomb/grave occupants forgets to leave behind any valuable knowledge to history!

UUUUUHH, Horsey got owned

Reminds me of the time I was in a linguistic anthropology class at college. Professor was an archaeologist, so I asked her that question. You should’ve seen the way she recoiled.
 
Unfortunately, I don’t remember her answer.