Difficulty adjustment would take care of handling the number of transactions, though it may take several days or even weeks to adjust, depending on how many miners cease mining and when the previous adjustment took place.

I have been expecting less efficient mines to start shutting down, a pity because those mines would probably soon become profitable again and the more miners we have, the more decentralised we are.

If Bitcoin does not go up then inefficient mines will certainly die off as ever increasing numbers of miners slowly erode their profit margins by increasing total hash power.