Rejuvenating an old tree is possible, albeit challenging on multiple levels, but it's worth doing if you can get good guidance or help. A great alternative is to take a few cuttings next winter and graft to a new tree- a youngster you buy; you can also send your clippings to a professional who will do it for a reasonable fee. But pears are the easiest to graft- you can do it yourself pretty readily. MileHighGirl for one has experience with this problem and somewhere there's a thread or two on what she did.