Of course they likely won't kill the tree.  They don't create a hollow, and
they really don't enlarge it.  In fact they may prolong it's life by
sealing the wood and protecting it from further rot.

Physically removing the hive is obviously out as it would de story the tree
(probably not want you want).  You could use the standard cone method.  It
works, but that can take some time.

I've been pretty successful at driving the bees out by heavily smoking them
(with newspaper with bee go on it in the top of the smoker).  Works best
with two entrances.  One to blow smoke in, and the other for the bees to
escape from.  (You can always drill another hole in the opposite end of the
cavity.  Eventually the bees will abscond and settle on a nearby tree or
branch.  You can they let another hive rob out the cavity before sealing it
properly.

I've only used this method twice, but it did work well when the bees needed
to be removed quickly, alive, and with little damage to the structure or tree.

If you aren't up to it  you might find one in your area who will.  (Though
I know few willing to do removals where I am and It's almost never a free
job.  It's not worth doing the job just for a unknown bunch of 'free bees').

-Tim

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