Cracked natural tooth beneath a veneer

It would be best if you could get in sooner, but you will be okay, as long as you try to avoid using that tooth.  I would recommend liquids and soft foods until you're able to get in to your dentist.  Your main goal should be keeping that fracture from spreading to your root.  Horizontal fractures usually do not spread, but ones that are more vertical can spread dramatically.  Good luck and I hope this helps. Follow me if you have more questions.Sarah Thompson, DMDReal Self 100

You may want to check with your dentist whether a post and core was done after the root canal to reinforce the tooth.  I would also have the bite checked.

Root canaled teeth are more brittle than vital teeth.  It really depends how badly the tooth underneath is fractured.  At this point my advice would be to not bite into anything and eat soft foods and keep the tooth very clean until you can see your dentist.