Could a small population of Tasmanian tigers have survived for the last 80-90 years? Possible. Maybe not probable but possible. Their historical range includes some pretty rugged areas without a lot of human activity. There have been repeated sightings including some from biologists and rangers whose credibility is high.
It would be fantastic if true!...................
Tasmanian tigers AREN’T extinct (or at least they won’t be for long!): Scientists unlock mysterious creature’s DNA - and plan to clone it bring the beast back to Australia:
https://www.dailymail.co.uk/news/article-5167733/Tasmanian-Tigers-come-dead.html