Abscess after wisdom tooth removal

My husband had his upper and lower wisdom teeth removed on his right side 5 days ago.  Over the course of time his swelling got worse.  Visited the dentist who said everything looked fine but prescribed penicillin just in case since it was the weekend.  Two days later (today) we went into the ER because the swelling was getting bigger and very hard to the touch.  It was an abscess, but the ER doc said it's too late to lance it or drain it because it consists of many pockets of infection.  He said this type of infection does not spread into the bloodstream or cause fever.  What type of infection might this be?  My husband was prescribed Clindamycin and was told it should start feeling better after 2 or 3 days.  The problem is he leaves for a business trip in 4 more days and it will last 10 days.  He's worried the clindamycin won't clear it up and he'll be in pain the whole trip and be away from his dentist and his doctor.  He's a tough guy, so I know he's in excruciating pain as he's not eating and he's sleeping all the time.  He's mixing 800 mg ibuprofren and hydrocodone as per the doctor, but it's not touching the pain.  I'm really wondering about what kind of infection this is and why it can't be drained right away?