Don't know whay kind of caterpillers you have. Every year about this time we seem to get invaded by saw flies which leave the polygonatums covered in gray caterpillers. If we leave them or miss them they absolutely skeletalise the plants.:mad We usually have to cut them down and burn them. Shame as they are so lovely. Thinking about getting rid if them unless we can find a solution. And they are so expensive in garden centres. I think your gooseberry bush will be ok and will just regrow. As for the caterpillers you might just have to hunt them down and destroy them