Cheryl, I am so sorry to read of your and Dave's problems. This disease is a nasty thing. I don't blame you for feeling discouraged. You have been through a lot. I think being a caretaker is harder in a lot of ways than being the cancer victim. Dave is your medal for the fine job you have done.
Unfortunately, there isn't any assurances or guarantees with this disease. We are all under the gun of a recurrance. All we can do is hitch up our pants and get on with what we have to do to fight it. And we can never let this thing beat us. As long as we battle it, we win. I know this is easy for me to say as I had only one time at bat so far.
You and Dave have done a heroic job to this point. All you can really do is continue doing it as long as you need to continue. You need to try to get some rest from the business. Either with a relative, friend, employee or whatever way you can. Balancing a cancer battle and a business can be very hard. Try to find someone to give you some relief. Also in your caregiving. If someone can help with that, I'm sure it would give you the chance to catch your breath and get ahead of the curve a little bit.
Please know that we on the board will support you as much as possible. Don't worry about spelling problems, as long as we can interpret what you are saying, we can deal with it. When I was going through treatment, I found that what worked for me was my involvement with my church family and my regular family.
Some of the folks on this board have had jaw replacements and other issues similar to Dave's. I just had a tonsilectomy, rad/chemo, and a neck dissection, so I can't comment on the extent of his surgery. Hopefully, the scan results will be a false alarm or easily treated.