Originally Posted by
MarLim
Even if you get a confirmed upgrade when purchasing the M fare, in case of Irrops, you'll find yourself again in Y, so there is a risk. The last time I used an SWU, I was very lucky, my flight the previous day got cancelled (airport closure due to snow), if I'd booked a day earlier, I'd have been OOL.
This is true, but generally in my experience, DL has been quite good with it - meaning that as long as your new flight has availability in business (not necessarily Z class), a call to the elite line can usually get this sorted out.
This is for Delta operated flights though as DL obviously can't make AF or KL open up award inventory.