I generally give my beers 14-21 days before checking gravity. Have patience. Yeast will finish when they are done. And +100 to Hokerer... Bubbles are not a great way to judge whether the yeast are done or not.
To answer your question, yes, eventually fermentation does cease. When alcohol levels get too high, or food is all gone, yeast will flocculate out or die off. But they will keep working for months, just at a vastly lower rate than the first couple of weeks.
Brettanomyces will work for months and more, cleaning up the leftovers from the original fermentation.