If Bumpers are not enough and the Top edges are too far gone, the remedy would be re-edging.
When a Bass is restored and the Top comes off, often there are pieces that are too distressed to be put back as they may crumble and break when the top is taken off. For this, the restorer can dohHalf-Edging under the Lip and replace the missing pieces above or re-Lip the entire Top if necessary.
Some of this 200+ year old Bass was entirely re-Lipped just under the Purfling line about 20-25 years ago and is invisible to the naked eye;
http://www.kensmithbasses.com/Double...ages/dodd2.jpg
This Bass is now being restored and only some of the Top was Lipped on the outside but completly half-Edged on the inside;
http://www.kensmithbasses.com/Double...esBass/137.jpg
If this Bass is opened up again in my lifetime by anyone other than the current restorer, the repairman will want to shake the hand of the guy who brought back life and strength to these Edges that were neglected for the past 192 years.
It is best to preserve these old Basses when ever repairs are needed. ?> When should one actually get the job done? As soon as you see things are turning for the worse or as soon as you notice something wrong like seeing fresh cracks starting!