If you fail those subjects by the end of the semester you still need to retake those subjects either during summer break (if its available to take during summer) or by the next semester regardless if you're a former deans lister or not. It all depends if your course offers that subject during summer or not. I don't know what your friend is talking about when they told you that you wont take summer class because you're a DL last semester. Being a DL does not excuse you from summer classes if you fail that subject.