Will my Japanese maple grow its leaves back in time?

Your Japanese Maple is a decidous tree that will lose it leaves during the Autumn and be bare all winter. We have several in the garden and they show no sign of new growh yet You will not see any new leaves appearing for several months yet.
As the tree has been infested by bugs (they maybe grasshoppers or not) I would be concerend that there might be grubs or eggs in the compost. I would wait until the begiining of winter then unpot the tree and remove all the old compost. You can then repot the tree in new compost or plant it in the garden.

If your tree doesnt survive I would go back and ask for a refund. It might be worth going back and getting her to write on your receipt that it was being fed on by 'grasshoppers'. The nursery should really offer an assurance. I'd be surprised if this will break leaf before your spring though as they drop leaves to prevent winter damage.

I'd also be cautious about 'overwintering' eggs and follow Bulbaholics advise.

Hope you have a lovely Acer come spring Dirk.

If your tree starts to grow again now, the new growth will not have time to ripen before winter, so don't do anything to encourage it to grow. So long as the tree is a reasonable size (i.e. over about 5 years say), it should survive well and regrow in your spring. If it starts to grow now, tho, the new growth will die back to the ripe wood in the winter. That will disfigure it a little in the shortterm, but you won't notice once it starts to grow again in the spring.