Haha, that is actually a very interesting question from that point of view. On one hand, you are already ahead as a layer because you have already taken plenty of futures money on (in this instance) Nadal or Federer to win the tournament, plus you will have laid an immense amount of money on them to win the individual matches they lost, especially in-play as they fell further and further behind and the odds on them to win began to look more tempting.
On the other hand, your turnover will be hit in some ways by the marquee players being missing from future matches, and there are definitely margins issues (slightly "fringe" players can become value, especially when it comes to offering competitive each-way terms) that come up when you have either one or a very small number of heavy favorites as you have now with Murray and Djoko.
As a tennis fan, though, it is truly a shame to lose the Fed, Nadal, and Tsonga this early.