There has been plenty discussion of this, of late, on the Pianotech
list (provided by the PTG primarily for professional piano
technicians).  The gist of the discussions, from those who've had
experience with this, is that the salt will stay in the felt under
the strings (in the bottom of uprights, I assume) and continue to
corrode them for decades, causing strings to "pop" in the middle of
the night (and at other times as well, one may presume).

So, if I were confronted with this, I'd hose down that area with
a directed jet of water to remove some salt, blot up as much water
as one can from the felt, then put a box fan in the bottom.  Or plan on
a restringing.  But I'd also print out these posts from the Pianotech
list, to provide as evidence to insurers that more damage may be
present than is apparent.

It should be remembered that the chlorine in the salt in the surrounding
wood may still aggravate corrosion.  (That's why chlorine bleach should
not be used to clean piano interiors --- as tempting as it is to do
sometimes -- because this will encourage a terrible corrosion to appear
long after the bleach has dried!)

Gordon Stelter

P.S. I have long had great success with using those concentrated soaps
now available (but no longer "Super Clean", because it has from the
smell, recently had lye added: a smell which remains) to clean piano
parts (which can be carefully dried later).  It is especially helpful
with player wippens, which can be put in a 5 gallon bucket, about a
gallon of the stuff poured in, shaken up, and then rinsed and the old
felts easily picked off, then rinsed some more, and laid out on a frame
(not in the sun!) with landscaping nylon mesh stretched o'er it.  When
dry, new felts can be glued on.  I have also found that this method
effectively quells verdigris on the center pins, leaving the centers,
once lubricated, "just about right".  This method may not be advisable
for fine grands (which ought to have their action parts replaced), but
I've found it effective for no-longer-available parts, such as these
wippens, so they don't "stick out" with a dark filthiness, once the
rest of the action has been replaced.