Have moderate sleep apnea W/severe O2 loss. Will treat w/CPAP & oxygen. In future is it possible oxygen can be withdrawn & Cpap alone be adequate?

Sometimes. Depends on whether patients have underlying lung disease and whether oxygen is also needed during the day as well. I have seen those that stay on oxygen and those that end up only on cpap over time.
Sleep Study. Your Sleep specialist will order a series of sleep studies. Your blood oxygen will determine what treatment you need.