I was thinking this same thing myself. I did some cursory research and apparantly there is an unidentified strain of a genus of thermally resistant bacteria, Microbispora, that survived the reentry and crash of the Columbia, as well as a strain of thermophilic bacteria, Thermoanaerobacter siderophilus, placed in basalt disks on the exterior of the Russian satellite, Foton-M4, with 1/6 of the cultures surviving.
Granted, Saturn's atmosphere is significantly thicker, but it still seems at least very vaguely plausible that certain extremophiles could survive or be whisked off into the less dense upper atmosphere, kept afloat by the potent winds and storms.
I realize at a certain point it all becomes a matter of "good enough", as there are very few, if any, practical ways to avert any and all risk of contamination, but it still seems like an odd and interesting subject. Love to hear if anybody knows anything more about this! :DDD
Microbispora - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3144675/
Thermoanaerobacter siderophilus - https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0132611