For all I know, the Pangu's axe is absolutely unique and cannot be regenerated, so logically, you can't do that adventure more than once at all.
For those adventure where you just go and bring some common stuff (like nectar) to some common sim, I actually have had similar ones several times.
For normal tombs (like, bring one artifact from that place, which happens to be completely worthless in all uses but in this adventure and spawns with the acceptance of this adventure even if you've been there a zillion times before on your own), I really don't know, and it may be that which opportunities you can do several times is a case-to-case study.
The tomb does not go "unexplored" again though, so it will not be as unique again as the first time at least.