it was showed before from a prophecy that the great dungeon will happen again, that is why they are looking for MC.
Now, through the phone call, ML and Guild leader is talking if the MC is mad but ML said, "No he is just upset" and then guild leader said either the MC hates ML and Seokyung Guild for bringing him out or his lack of reaction is because MC never expects anything from others. so like MC is nonchalant and honestly doesn't trust anyone. So ML is having deep thoughts about that latter, and he actually prefers MC to hate him so that he can apologize but MC is nonchalant.
Anyways about the vacation you are saying, he did technically have a vacation for 10 years, and for MC after the will he wants to die. There is no Vacation in mind for our MC.
plus from how MC is written he is not someone who will ignore a big big problem like the Great Dungeon appearing again so by the plot, MC will enter a dungeon whether he likes it or not.
Let me to be clarified to see If I understand, please correct me If I'm wrong. After the phone call, he basically statement that you have to do it it something you hated it because that is the responsibility of being strongest person to fight for the world. Is he referring to himself or MC? If he referring to MC, then why he said that he won't let him enter to dungeon or anything even if the system decides and required from him even if that strongest person's duty. To be honest, MC have done enough to save the world before why he must save once again if he went out hiding after so many years, just bc he saved the world and expected him to fight again.
Just leave this man rest and don't expect somebody to work until they die. Seriously, everyone needs vacation after they went through or served their time.