Traffic making a missed approach will get vectored straight back downwind for a truncated circuit, can still add about another 40 or so track miles though. Won't get anything much quicker than that unless there are fuel issues.
They won't go all the way back to a hold unless they themselves want to if the missed approach was for technical reasons as sometimes happens.
They will get an extra mile or so in front of them second time around...
As has already been mentioned, better to land 40+ an hour with the odd missed approach than 35 with none.