If they still existed we would find evidence in the form of carcasses, bones, poo or kills.
I would love it if they did still exist though.
https://en.wikipedia.org/wiki/Tasmanian_devil > Tasmanian devils can eliminate all traces of a carcass of a smaller animal, devouring the bones and fur if desired.
The poo one is interesting - no matter how hard I google, I can't find an image of thylacine shit, so not sure how you'd differentiate it from other animals' scat.
>They are also found near roads where roadkill is prevalent, although the devils themselves are often killed by vehicles while retrieving the carrion.
From the Tasmanian Devil wiki page.