Depends. Some stab wounds to the chest don't break the subcutaneous tissue or muscle and may just need stitches. Others can hit lung only, only requiring a chest tube until the hole seals. Arteries in the chest wall can bleed into the chest cavity, but are repairable. Hits to the heart and great vessels can be rapidly fatal. For all chest penetrating trauma, rapid eval and treatment is essential.
Depends... Depends on depth and location. You're better off not getting stabbed. If you have no choice, pick the right chest. The heart being on the left can prove to be fatal. Stabbing muscle or rib is survivable. Puncturing lung may pose a threat if pressure builds in the chest. If any large vessel is cut, game over. It is very hard to put percentages but a literature review places you at high risk.