If it’s a small slow leak, you can simply put up with it and keep an eye on your oil. If it’s leaving puddles, it needs to be addressed. It’s not a repair the average vehicle owner can do, and it’s not particularly cheap to have a shop do because it’s labor intensive, but on a low mileage rust-free truck probably worth having done.
With good maintenance you can expect the drivetrain to last to 200k and beyond. The 4.2L Essex V6 was very reliable for the era, although as a legacy engine low horsepower.
It’s fine. When you finally get the old pan off just clean it well, the only passage into the engine itself (oil pickup tube) is screened off so no worries about pests, and it’s unlikely to have rusted because of all the oil coating everything in there. At worst surface rust, which you can just knock off during the cleaning process. There shouldn’t be any way for water to get from your holed oil pan into the engine itself outside of just being straight flooded.