My general opinion is #2 that a large majority of builds should remain protected, aka no griefing allowed. The current map is so large that I don't see a reason for players to take items, edit, grief, or move into an inactive player's build(s). While it is not guaranteed a player might return after multiple months of inactivity, I can't imagine it being a positive experience for a player to log in after a few months and find their builds or items griefed or taken and admins tell them "sorry, you needed to be more active"
The exception I could see argued are features or locations which benefit all active players such as the end island, public shop world, nether rail, server xp farms. In this case, I think there needs to be a balance between leadership and player ownership depending on case by case, end island makes sense for leadership to "own" as in don't let players claim the island but allow players to make minimal changes (wither farm, obsidian farming, stairs to the floating portals). Xp farms are currently player owned, but what happens with say the current situation with the enderman farm which had a public warp, does an inactive owner mean the only viable solution is to build more player owned enderman farms, or does leadership step in and maintain it, least until that player decides to return?
Edit: Thinking on it, there is still the situation where someone inactive didn't have a claim, does get griefed, and then returns but the grief happened long ago. I think it is a better reaction if admins still attempt to help the player fix the damage any way they can, maybe even help provide the player some items and food to help them get back on their feet.