Claritin does not dry up fluids. Claritin is an antihistamine, and prevents the release of histamine in the presence of allergens. Histamine causes tissue edema, among other things. But nothing about claritin will dry up fluid which is already present in the middle ear.
The presence of persistent fluid in the middle ear is suggestive of, but not diagnostic of, some degree of persistent obstruction in the Eustachian tube. But the ability to pressurize the middle ear is far more accurate than the presence or absence of fluid, in terms of determining Eustachian tube function.
What is really concerning about this case is that the original injury was a reverse block. They're uncommon, as the rising pressure tends to push the Eustachian tube OPEN (whereas on descent, pressure gradients tend to hold it closed). But the only way to diagnose a reverse block is to descend and then ascend . . . and once you're at depth, you're committed to ascent, no matter what damage you do to your ears in the process. For this reason, I'd be fairly conservative about putting myself in a position where I might have to find out that I'm not fully recovered.