Airbox, rear wheel and swingarm if the fit is anything like the Pro-Link models. Much easier to shift the engine I think.
BUT unless it is a show bike I think I would either patch it, find a good one and change it the next time the bike is apart for something else or change to a different tank in another location (there are a couple of threads about doing that).
BTW: The only time the tank is close to pressurized is if something happens in the engine like overheating enough to boil over or a blown head gasket, either of which can send more coolant to the tank than normal but that's why there is an overflow hose.
I'd be more concerned about what could get into the tank and be sucked back into the engine if the crack gets wider.