If there is a chance the Yellow will change hands or for that matter that a podium place may change they will race from the start. Historically Eddy attacked on the last stage in 76 and did not concede the victory until he had been caught. Hinault won a final stage when the rider in second attacked and he chased.
Do remember that the final stage these days is flat which means there is little chance to get any real time. There really is much more time in time bonuses than there is any chance of getting from a gap. With 2 6 second intermediate sprint bonuses and 20 at the finish this is what contenders would look to. So strategy could get a bit unusual. Picture a big rush for the first time bonus, but if the 'wrong' guy wins the stage turns into the normal parade. If the 'right' (e.g. trailing) guy wins then an even more hottly contested second sprint.