In 2003, Venus didn't play any warm-up event and reached the finals of the AO! I wouldn't be too worried for next year either!
And long lay-offs are never a one-way thing. It might hurt the sisters (cuz of rustiness) but it will certainly hurt their opponents too. When the sisters will be back, all players will have forgotten how much powerfull they are and might actually have difficulties to re-adjust to the sisters' game!
Predict winners all year for all tournaments at :
It's fun, friendly and free!!!!
"Of all the things I've lost, I miss my mind the most", Darwinian Motto