Papa is 86 with 3 leaking valves, no surgery due to age. low bp and chronic chf. no increase in lasix (furosemide) due to bp. how long can this go on?

Not predictable: With proper compliant medications, diet and support, Papa could live for months or even years. There is no good predictive model and it is in the hands of a higher power regardless. Obviously we are mortal so you should cherish the time you have now and work with your physicians and Papa to make him as comfortable as possible while avoiding things that might make his CHF worse.