I handled an old revolver today that had no finish left on the last two inches of the barrel, but the rest of the gun was top condition. Most likely left in a wet holster? Any how, to have this gun reblued, would the barrel have to be removed? Would the smith be able to do this without removing it?

The barrel can stay on.

I blued the entire barreled action of 98 Mauser in 1971 at my kitchen table with Birchwood casey cold blueing solution. I made sure all traces of grease and oil were removed ferm the barreled action and removed the bolt and plugged the muzzle and breech with a piece of wooden dowl rod. I had a long chicked feeder about 4 inches deep and a little longer than the barreled action and put in on the kitchen stove with the barreled action and boiled it until the barrel was hot enough that it flash dried when removed from the water. I then put Birchwood Vasey cold bluing solution on cotton balls and rubbed it on the barreled actionand after it was good and dry I went over the barrel with 000steel wool. I then repeated the process over and over again. I don't know how many times I repeated the process but when I was done the bluing was black and shiney and it still looks as good today as when I sporterized the rifle for my brother, You could remove the cyclinder and the grips and you probably have a pot you can use to heat the metal. If I were going to do it I would do the handgun frame by its self and then do the cyclinder and cyclinder rod seperately. This photo shows how nice the blueing got with this simple process. If the gun has rough spots you could go over it with very fine emory cloth before you start the bluing process.

my experience with bc has been good

Depends on the revolver and what you want it to look like, when it is re-finished, how long the blue will last, etc. If you want a palomino pony look, cold blue works great for a painted horse look or for newbies or novices.
Old Smiths and Colts have a high polished finish with a hot blue that is actually black.
When I am examining guns to take in, I use a can of spray bore solvent and a paper towel to "clean" them, owner is very surprised when I wipe that nice finish right off.

Sorry, you sir are full of beans! That rifle in the photo Im posted was reblued by me in 1971 and irt was hunted with for all the years between than and now and still looks as good as it did when I reblued it.

Number one thing I've learned DIY bluing other than REALLY degreasing is critical is the smoother the metal the better the bluing. Don't rush the polishing.

There's no competition between hot and cold blue. Hot blue actually turns the surface of the steel into black oxide and provides surface protection by holding oil in the pores. Cold blue is for touch ups only.

From my experience, have an expert do it and match the correct / original bluing type.

Well, if you can use cold bluing to your own satisfaction then go for it....personally, that never worked for me, especially on an entire gun. Two quick tips to help are try using lighter fluid to de-grease and also a propane torch to warm the metal up.
I restore and re-blue a lot of guns so of course I have hot blue tanks. Make no mistake, hot bluing can have it's "issues" too. But, in general it will always produce a more even, darker and way more durable finish.
As far as the original question, "can you blue half of a barrel???" Yes, many times I have had guns with a bare metal issue where the rest of the gun was fine and just didn't need polished. I was always surprised to find that it came out a perfect match and blended well for me.

BG, that is 100% correct.