Yes, paintball will wash out of jeans. The balls used in paintball games are designed to be biodegradable, water-soluble, and hypoallergenic and will not leave permanent stains on any surface. Therefore, if you get your jeans stained with paintball, it will come out.
It will be better if you treat the stain as soon as possible before it gets deeper into the fabric. If this should happen, you may end up spending extra hours cleaning the stain.