TLDR: the 5th Amendment is big dynamite, almost entirely made of unintended consequences. There are much better ways to do this.
Anyway, Bob swore to tell the truth, the whole truth, and nothing but the truth. That prohibits him from giving either of the answers he is being railroaded into, so he should say "I cannot answer in this format".
Bob needs to get help
At the very least, Bob should shoot a "What the heck???" glance to Diane, the opposing counsel. This will clue Diane in that she should either be ready to object, or should ask Bob more questions about the subject matter.
Because when Alice is done, Diane absolutely can say "I have more questions for this witness." And there's nothing Alice can do about it, except ask more questions of her own.
If Alice revisits the same question, Diane can object that the question was already asked and answered. Alice can do the same to Diane, so Diane would need to ask in a different way or take a different approach that asks Bob to fill in the details.
Bob should also signal to the judge that this question is not answerable like that. The judge wants just what Bob swore to, the whole truth, and the judge will back up Bob, and perhaps even intervene, if he feels Bob is being railroaded.
It would be bad for Alice
That would put Alice in a bad position, because then it would become apparent to the judge and jury that Alice is laboring to twist witness' words to change their meaning. They would think about other times she framed a question like that, and the witness answers would be mistrusted. Creating jury distrust in the process is exactly why judges don't permit much of this.
Pleading the 5th? Bring your checkbook.
The problem in civil trial with pleading the 5th is that the 5th Amendment does not grant immunity to litigation. Bob would be promptly added to the defendant list.
Alice would argue that if Bob's actions relating to that vase are so heinous as to be actually criminal, then it's more likely than not that Bob himself is responsible for the breaking of the vase. Bob broke the vase in the commission of a crime.
In civil court, the burden of proof is "more likely than not".
Alice will argue that is not in the purview of this jury to punish Bob for the crime, and indeed that Bob may well escape prosecution for this crime, since he has not even been a suspect up until now. So the jury should do all they can to hold him to account.
Alice could also use the ordinary discovery process she is entitled to, to thoroughly explore for evidence of Bob's crime, in full view of the jury. She would soon have the jury thinking Bob was Al Capone.
This changes the landscape for Diane. Bob isn't Diane's client. By throwing Bob to the wolves, she exonerates her client. Bob has no friends here, and isn't entitled to counsel who could cross examine or object... at least not until his name is added to the defendant list, and Alice could "game" this to weaken him.
What's Bob to do? Assert that he should have counsel at the defense table because he expects to soon be named as a defendant?
A more worrisome matter: The judge would have the opportunity to refer the matter to the district attorney for criminal prosecution. DA's have broad latitude over which cases to bother prosecuting, but they take judge's referrals very seriously.
So this will likely cost Bob the price of whatever is being litigated over, and possibly much, much more. As such, this is a very foolish way to approach the problem. Bob could achieve the same end cheaper and with no damage to his reputation simply by offering to pay Alice's client to "go away" (settle the matter with prejudice, meaning Alice's client can't bring another action in this matter). He would then be a "white knight leaping to the rescue".