Sorry if this question is too basic, but as I learned about how supernovae are means of producing heavy elements I began to wonder "What would happen if stars didn't explode, i.e. undergo supernova"? Hydrogen and Helium would definitely dominate element abundance at a higher level, but how much carbon and other heavier elements be produced? Are there intermediate stars of enough mass that we could reach all the way to Iron?
Now what would happen if stars never reached the planetary nebulae phase? Would the only elements present be Hydrogen and Helium?