Oooh, this one is interesting! Well...I think any sole survivor would definitely try to get back to the Obra Dinn if they knew what's good for them (because good luck trying to get to the Canaries on your own), but I think where the main divergence lies would be this: would Galligan attempt to bring the mermaids onto the rowboats and back to the Obra Dinn, thus leading to all the chaos that follows afterwards? Or would he just bring back all the corpses that remain (the spears that stabbed O'Hagan and Hong would be interesting evidence)? Yet...Galligan is on the tinier and frailer side, so I don't think that he would be able to actually pull up any of the mermaids, especially with how damp their long hair is and then their massive tails. Now, in this case, he wouldn't really have any bargaining chips like Nichols did to beg for mercy when encountering the Obra Dinn, and he could try to lie and say that Nichols coerced him into participating in their little expedition...but ultimately, I think he would also meet the business end of Tan's rifle... 🥴