But keep in mind that the example you described above is quite unusual (the device gets broken in the middle of an I2C transaction) and I don't think that the I2C standard supports that such situations are correctly recognized. So it might be of an academic interest how the AVR hardware reacts in such situations but it's not relevant for practical use in my opinion.
Very much practical; but, the issue appeared as we could not authentically resolved the roles played by Wire.requestFrom() and Wire.available() functions in respect of the figures they return. I have firmly recorded the tentative answers you have given voluntarily to my questions, and I wish that I will make responses based on true measurements creating a genuine fault in the active TWI Bus running at ~490 Hz and ~2 Hz speed (SCL frequency = (clkSYS/256)/(16+2(TWBR)(TWPS)) = (16000000/256)/(16+2255*64)) =~ 2 Hz). The experiments are in the process where I have bypassed the Wire Library functions where I could; instead, I have employed register-based instructions. However, the Wire Library helped me a lot to debug/develop the low frequency TWI Bus Experimental Setup.
When all kinds of minds -- poetic mind, prophetic mind, philosophical mind, critical mind, rational mind, pragmatic mind, scientific mind, and technological mind come into an association, the divine (natural) mysteries are resolved to a great extent.
We are involved in the studies of TWI Bus which is the creation of a number of scientific/technological minds. It is not a natural phenomenon, and yet it has appeared as a mystery to a few pragmatic minds who want to correlate the observed results with what had been set at design time by the TWI Bus Architects.
We can try to validate our conceptual understandings with the available test gears that we have in our hands. The aim is to satisfy merely our individual thirsts.
BTW: There are many many good reasons for liking the Wire Library. I like it. The three methods : beginTransmission(), write(), and endTransmission() when placed one after another bring cool to the eyes. They have replaced so many register level instructions that the Wire Library has made TWI Bus programing job easy and comfortable. The developers team deserve great appreciations!! By talking about the return value of endTransmission(), I was actually referring to the highly abstracted feature of the method.