My preferred solution is to have an electric AI as backup. However, probably the most dangrous thing of all is the time it takes to recognise that you have a vacuum failure. If this is too long you are probably in an unusual attitude which you are going to have to get out of partial panel or using the backup AI all in IMC. (A VMC vacuum failure should be a non event)
There is no doubt that an IMC vacuum failure without backup is a full on emergency ( and could be one even with backup).