would i get in trouble for leaving the country while on sick leave?

so my friend is currently studying at UWA on subclass-500 student visa. He was invited to a wedding of his relative, but it happens on exact day he had a day worth 30% of his mark. Not going to the wedding is not possible, as his asian family is strict about family gatherings especially things like these. the only viable option he seems to have is taking a sick leave(EVA), and leaving. His family also wants him to be there for a whole week, so he will leave country for a whole week during his study period. Question is, are there any other options, to avoid lying? if not, how likely it is he will get in trouble in university? and the one he is most concerned about, could there be any problems regarding his visa?
thank you all in advance, tell it as is, no sugarcoating