Disclaimer: I haven't read any the technical details of how this works.

In decentralized systems, shouldn't nodes suffer repercussions for dishonest behaviour which outweigh the potential gain? Which could mean (complete conjecture here) the archaeologist node would no longer be able to participate in the network, and would stand to lose out on more money that way.

I have no idea if the sarcophagus protocol/network actually provide the correct measures to ensure nodes can't be incentivized to do this. I would hope so though, it's like 'decentralized network 101'