Very muddy case, I did not fully understand it actually. If he won the trial, then why didn't he recover his expenses at the expense of the losing side?
But let's assume this is a purely theoretical question. I know that such dilemmas often arise in civil litigation, since there is always the word of one side against the word of the other side and the presumption of innocence does not apply. That is, you must prove that you are innocent (what the opposite side accuses you of). Often such cases end in nothing - that is, party A cannot prove their statements, but party B cannot prove that these statements are false. And in the end, the one who tried to protect his reputation loses time and money (for lawyers and other expenses), but cannot "restore" his reputation.
I don't know how to solve this dilemma. You need to look at your financial capabilities and how much your reputation "brings you money" - if you lose income after losing it, then you need to protect it (but again with reasonable spending), and if this does not affect anything, then it might be worth going through by and forget about it.