Should be no issue at all with head gasket failure,veggie is a much slower longer burn than derv ,hence runs quieter,also coupled with veggie being a superior lubricant than derv.Engine tends to run cooler.
As it is more viscous than derv,it is kinder to the injection pump mixed with some derv to drop the viscosity a bit(twin tanking best of all),but Bosch pumps are extremely tough,so most do not bother.
Veggie having better solvent properties than derv,can loosen up ****e in the tank and lines and dump it in your filter clogging it-best to carry a spare in anticipation-but this does not always happen, depends on the state of your tank.
Ring gumming can rear its head after extended use(talking years of veg only use) but this is easily sorted with some water injection,mate of mine did this with the windscreen washer pump attached to a spray bottle nozzle,fired into the inlet manifold (AFTER TURBO) a few blips on the switch at 60mph on the open road sorted out all his probs.
Most of these problems seem to occurr if you leave your diesel ticking over for hours in traffic jams-diesels after all are designed to work and work hard