Technically speaking you are a master tenant, but you cannot demonstrate that you are an original occupant because you moved out for six years.
Welcome to Rentpocalypse 2012! Have a seat, but don’t stay too long.
San Francisco is expensive and many landlords these days want to cash in on the new Twitter/tech boom. One of the easiest ways to remove rent-controlled tenants is to sue them for illegal subletting.
If your lease requires the landlord’s written permission to sublet, get the landlord’s written permission and have at it.
The bridge you don’t want to burn is a bridge to nowhere. You were never going to get a good reference from your landlord, Captain Ahab, anyway.