I'm wondering what in-game experience you may lose if you decide to play offline-only in Dark Souls 2. Of course you can't invade or be invaded or request for help but I'm more concerned about the story / NPC / secrets. Do you lose something by playing offline?
I haven't discovered every last secret in the game, so I can't claim to be authoritative, but based on what I've experienced in this game so far and from my experience with prior games in the series:
- You can't participate in any kind of co-op or PvP, obviously.
- You can't read or write messages.
- You can't meaningfully participate in (or earn rewards from) any convenants that require PvP or co-op interaction to do so.
- Certain boss fights or protected areas that are designed to bring in other human players as opponents will probably use AI-controlled NPCs in those players' place.
- All of the story/NPC elements are almost certainly still accessible, as NPC progress is solely based on your solo exploration and interactions, which are mechanically unchanged in offline mode. This is also how it worked in both previous Souls games.
- The sole exception to this may be any covenant NPC dialog or events that are only accessible after you've ranked up in one of the aforementioned co-op or PvP-oriented covenants.
The answer above basically sums up the consequences of offline play. However, although your in-game experience will be different and you will be losing out on multiplayer related activities, playing offline should give you a much greater sense of satisfaction and instill into you a greater sense of excitement. The reason being is that the game is MUCH harder if you play offline. In Dark Souls II, the pvp is generally concentrated in certain areas and thus, you are mostly able to co-op with other people without consequence. By co-oping with other people, you are able to net experience by traversing throughout another person's area as a white phantom (there is no consequence upon death), reverse the consequences of death in your own world by helping other people as a white phantom, get help with your own area bosses, and are able to level up extremely fast by farming bosses. Generally, by playing offline, you will be able to truly appreciate the Dark Souls series for its difficulty and feelings of hopelessness, despair, and desolation. In the end, what I mean to say is that you need to limit co-oping to truly experience the greatness of the Dark Souls.
I'm not exactly sure how accurate it is to say you can't rank up offline...I hit Lvl3 offline in Bellkeeper's off the Mad Warrior NPC spawn alone (which is EXACTLY why that NPC exists) & in NG+ it's a fact you can get Sunlight Medals off the Falconer enemies that start showing up in NG+ & beyond. I've also heard that killing Red Phantoms (I THINK it was) count towards Blood/Sentinel/Blue rankings, though I've not confirmed, plus you can get Invader-relevant tokens/kills through announced invaders (such as Bowman Gumfry/Doors of Pharros) & farm them quite effectively as the invaders respawn in NG+ (12x just like regular enemies). Point being I REALLY wouldn't be surprised if there was a way to Rank up EVERY Covenant offline...it'll likely just take longer (looking at YOU, Dragon Remnants)~
If you are simply seeking to Plat/100% the game's Trophies/Achievements & are concerned about ranking for the couple spells that SEEM only available via ranking as a Blood/Sentinel (Chaos Firestorm, etc) & think 500 sucks as a number, Wellager sells them once you find him in NG++ (in case you didn't know)...hope that was useful info in any way~