No - it's so unfair to the other kids and staff! He's contagious. This is how your kid got sick to begin with - someone who didn't stay home.
I'm happy he doesn't feel sick - but it's irrelevant from the standpoint of school. His fever should be 99 or below with no meds for 24 hours. If he were older, I would say to get some work sent home by the teacher, but at 8 I don't think it matters. You can email to see if there's anything simple she can send home via email, although it's very short notice. Or you can ask for something to be sent to the office and you could take him in the car to pick it up (but he doesn't go inside. If you can't have someone watch him then have a friend pick up or see if it can come home with a sibling if they're in the same school, or in a neighbor kid's backpack. Read books to stimulate his brain and give him more sleep/rest than he wants. I'd keep an eye on that active nasty cold sore too.
Use the boredom to your advantage - next time he doesn't want to wash his hands or go to bed or drink enough fluids, say, "Remember how you were so bored at home?"