Chia Seeds do eventually go bad but it takes over 4 years for the Chia Seeds to go bad where you shouldn't eat them.
Chia Seeds are generally good for up to 4 years once you purchase them so as long as you use the Chia Seeds within those 4 years you'll be okay.
If you do happen to eat some bad Chia Seeds the worse thing that would happen is you get a stomach ache, diarrhea etc.
But it won't harm you really to eat bad Chia Seeds.
Most people will use the Chia Seeds long before 4 years but if you don't it's safe to eat them until at least 4 years.
If I had Chia Seeds that were older than 4 years I would throw them out just to prevent getting sick.