Quite possibly - always safest to empty out the pot, getting rid of the old compost, give the pot a good scrub, then use new compost.

Yes give it a good start with some fresh compost, the grubs sound like vine weevil grubs, if you have any other pots and the plants are not looking to good then check for vine weevil.

You say you see white grubs in the old soil take the above advice. If the plant has not come from a reputable source I would wash its roots to remove all of the nursery compost before repotting in fresh compost. You can kill those grubs with a vine weevil killer but it is easier to squash them if you came across any. You should not put the old untreated soil in the compost bin or in the garden without treating it first even if you cannot see any more grubs.