veteran rocker 's surprise guilty plea at the eleventh hour .
phil rudd was set to stand trial on ` threatening to kill ' and drugs charges in nz court on tuesday .
in the worst case scenario the 60-year-old could face up to 7 years jail .
he has already been replaced by chris slade on the group 's ` rock or bust ' world tour due in australia in november .
rudd will be sentenced on june 26 .