Not true.....
The distance is too short for him to have anyone over take him........that's why no one will try.
Greg Lemond won the race on the last day, I think he had something like 44 seconds to make up which is definitely doable.
Now unless they have changed the rules, it is possible to win the last day...usually the lead is unassailable so that's why he has "already" won it.
But the distance is flat, no one realistically will get to make up 2 minutes on the last day. The team would protect him should anyone try.
However as I say, it can be done...(unless the rules HAVE been changed but I very much doubt it). It is possible I suppose that he could fall off early doors, break something and not be able to finish in which case he could lose the race. If it is a mechanical thing, with the support cars and that, it's doubtful that he could lose that time and generally the race would slow down until he got back into it. The race has ALWAYS done that even in the other stages. If the leader suffers a breakdown or a crash the rest of the peleton would slow the pace until the leader got back. It's the gentlemanly thing to do.
Sicknote is the expert on this so he can verify.