How does VSG work if you've previously had an incisional hernia repair with mesh?

Generally it should not be a problem to have a sleeve after incisional hernia repair, even with mesh.  You do not need to worry about the insufflation of the abdomen stretching the mesh.  All laparoscopic incisions are small and do not disrupt the integrity of the mesh.  The only incision that is a little larger is the one that the resected stomach is removed through.
Should be fine.

I have done gastric sleeves in patients that had a previous incisional hernia repair.  Ideally you want to do the sleeve laparoscopically.  Yes, there will be a lot of adhesions, but an experienced laparoscopic bariatric surgeon can get it done with the laparoscope.  No, the mesh will not stretch.  Yes, the mesh can be re-sewn and it will heal fine.  Consult with an experienced bariatric surgeon in your area.  You will be fine.

It is hard to say for sure without knowing where on your abdominal wall the mesh was placed, but I have operated on numerous patients with prior hernia repairs and it isn't a challenge that can't be overcome.   If the hernia was from a prior C-section, meaning lower on your abdominal wall, then the laparoscopic port sites for a VSG should not interfere.   Inflating the abdominal cavity will not damage the mesh or cause it to tear away.   Pain is always hard to anticipate, but hernia repairs are often quite painful, so there is a good chance that a laparoscopic VSG will be less painful, but nothing is for certain.