So each rank gives you certain bonuses (immunity from trap damage, the ability to teleport to different zones, the ability to access your mail, etc) at different ranks. What get at each rank is best explained by neverwinter itself in game.
When your VIP expires, you lose access to all of the VIP bonuses. The good news is that it remembers which rank you were forever. So, in your example, if you were rank 2 when it expired. If a month later you repurchase a month of VIP then you would be Rank 3.
If by nice **** you mean actual items like mounts/enchantments/etc (which mainly would mean the items you get from lockboxes as you get one key a day while VIP), you keep those forever.
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When your VIP expires, you lose access to all of the VIP bonuses. The good news is that it remembers which rank you were forever. So, in your example, if you were rank 2 when it expired. If a month later you repurchase a month of VIP then you would be Rank 3.
If by nice **** you mean actual items like mounts/enchantments/etc (which mainly would mean the items you get from lockboxes as you get one key a day while VIP), you keep those forever.
I'd be much more interested if I could go lifetime like I did in STO
You bought rank 1
Your 30 days of vip is up after purchasing rank 1
You renew your vip status by purchasing it from the zen store. Whether you buy another rank 1 3 or 6.
Depending on what you get you will be rank 2 or higher no matter what. I found the vip system very confusing when I first started.