This doesn't add anything new but you may find it of interest.
TROVE has an announcement of the arrival of the ship
Cuthberts from Greenock.
A Renwick is in the passenger list.
http://trove.nla.gov.au/ndp/del/article/4783119It's really difficult to trace some of the young men who came to Australia and died with no family and, perhaps, few friends, or at least few friends who knew the family background. There may have been no-one who knew any details about him, or able to identify him; or, as you say, he may well have moved on from Victoria. (Australian BMD records are kept by each State - some have on-line indexes, some don't.) I do not see a death listed in the Australian Death Index but that index has many errors and omissions.
Is there any indication of the date of his death on the MI? If the parents were informed of his death then it would seem likely that there is a formal record - somewhere
Judith