I actually did this with a pair of raws that had a large crotch blowout a few years ago. I used Tear Mender as recommended in this PTO post and it worked out surprisingly well. I wore my raws nearly every day for a full year after that and there were no signs of it falling apart, so I expect the adhesive would last a very long time, if not the entire lifespan of the jeans. The only thing I will warn you about is if you use too much (like I did) the adhesive might soak through the fabric and be visible on the outside. All you have to do is scrape it off (I used a dull knife) before it sets completely and it'll be gone.