What was the fate of the Duchess in Robert Browning's "My Last Duchess"?

The last few lines provide us with all the evidence that we need:

Whene’er I passed her; but who passed without
Much the same smile? This grew; I gave commands;
Then all smiles stopped together. There she stands
As if alive . . .

It is implied, but not strictly spelled out, that the Duke had his late wife murdered. In his conversation with the court emissary, the Duke unwittingly comes across as a jealous, controlling man who couldn't handle his wife's flirtatious, effervescent nature. The Duke is very much a man of his time. He lives in a traditional culture in which men think nothing of having their wives and daughters killed to preserve their families' honor and reputation. So, even if the courtier understands the Duke's cryptic reference that he

gave commands;
Then all smiles stopped together.

According to the words of the widower Duke, the Duchess, as lovingly and smiling as he would portray her was also quite salacious and flirty with people form court. When we get to the point where the Duke explains her demise, we encounter an enraged and hurt man who may have been cuckolded, and humiliated. In the Duke's own words, he made the order to kill the Duchess.

Hence, we read the words

I gave commands. Then all smiles stopped altogether.

In Robert Browning's poem "My Last Duchess," what happens to the duchess?

I gave commands;
Then all smiles stopped together. There she stands
As if alive.

"My Last Duchess" by Robert Browning was written during the Victorian period. Much of the poetry written during this time was experimental because this was the time of the novel. Browning utilized realism and psychological implications often with callous language. The Romantic poetry directly contrasts with the power of Brown’s writing.

Browning based this poem on an actual historical duke, Alfonso II, whose wife was one the Medici family.  Lucrezia, married to the duke at 14, died in suspicious circumstances.  After she died, the duke negotiated and married another aristocratic girl. 

This is a macabre poem with a psychopath as the narrator. The duke has many unsavory qualities: jealousy, envy, suspicion, evil.  He believes himself to be an art connoisseur, so the poem circulates around a picture that the duke had painted of his last wife.

In the poem, the duke has asked the marriage negotiator/servant of the Count to sit and examine the painting of the last duchess.  The duke loves the painting by a famous painter of the time. He keeps the painting covered and only shows it to those he chooses. 

In his poetic monologue, the duke gives his reasons for his displeasure with his former duchess:

• Her joy spot (blush) should be reserved only for her husband, yet it was too easily called forth.
• Her heart was too big and with little difficulty made happy (Was she not serious enough?).
• She looked at everything, and it impressed her.
• Regardless of who or what it was, it drew from her the same favorable words.
• She thanked people for gifts as though they were as good as the gift of an aristocratic 950 years old family name.
• She smiled at others in the same way that she smiled at him.
• If she had made an excuse for her behavior, then he would not have given her a lesson. 
• Her excessive behavior continued and grew. 

The duke gave commands and that ended it. 

Is the duchess dead or alive? Does Browning give the reader clues to answer the question?

In the first line of the poem, Browning gives his answer and repeats it later in the poem:

That’s my last Duchess painted on the wall,
Looking as if she were alive.

(1)Ironically in the picture, the duchess appears to be alive. The key is that she only looks as if she is alive.  Inferentially, the reader must draw the conclusion that the duchess no longer walks the earth. (2) By the duke referring to her as his last duchess, again inferentially it would be safe to assume that she has passed away.  (3)The last clue would come from the fact that religiously divorce would not have been allowed in the time period; thus, if the duke is negotiating a new marriage, the last duchess must be dead.

This psychopathic aristocrat believed that his wife should only look, smile, and blush for him.  Since she was too friendly with everyone, he killed her. Now, he is courting another aristocratic girl.  If the Count were smart, he would take his daughter and hide.